Airbag inflator and an airbag apparatus

ABSTRACT

An airbag inflator includes non-azide gas generating propellants, surrounding an ignition device, disposed inside a housing. The gas generating propellants are surrounded by a coolant/filter device having a pressure loss of 0.3x10-2 to 1.5x10-2 kg/cm2 at a flow rate of 100 l/min/cm2. A space is provided between an outer periphery of the coolant/filter device and the housing such that the combustion gas passes through the entire area of the coolant/filter device. The coolant/filter device is also surrounded by a swell suppressing layer which prevents the coolant/filter device from swelling due to a combustion of the gas generating propellants.

This application is a divisional of co-pending application Ser. No.08/829,314, filed Mar. 31, 1997, the entire contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

This invention relates to airbag inflators and systems utilizing samefor enhancement of driver and passenger protection, including sideimpact protection, in motor vehicles and the like.

BACKGROUND OF THE INVENTION

Conventional airbag inflators have relatively complex structures withelements such as forged housings defining internal ignition, combustion,and filter chambers by integrally formed and/or welded internalpartitions. Furthermore, coolant structures, such as filters formed fromheat conductive materials and the like, in many cases require theforegoing structural complexities in order to withstand the temperaturesand pressures generated within these inflator structures.

Many of such conventional inflators use azide based gas generatingmaterials such as sodium azide based materials which have relativelyhigh burn rates and undesirable toxicity levels and products ofcombustion such as mists and ash associated therewith.

Accordingly, there is a need in the prior art for more simplisticinflator structures, such as those formed from sheet metal havinginternal chambers formed in part by improved coolant/filter structuresand utilizing non-azide propellants having controllable burn rates, gasvolume production, internal pressures, and internal temperatures toincrease the effectiveness of airbag inflators while reducing the sizeand the cost thereof and producing lesser amounts of undesirableproducts of combustion such as mists and ash.

The azide-based gas generating material (NaN₃/CuO, for example) has arelatively high linear burning velocity of about 45-50 mm/sec under thepressure of 70 kg/cm². Because of the relatively high linear burningvelocity, the azide-based gas generating material, even in the form ofrelatively large pellets or disk-shaped pieces with an excellent shaperetention capability, can satisfy the required complete combustion timeof 40-60 msec when used, for example, in the airbag inflator for theairbag at the driver's seat side.

Non-azide gas generating materials, which have been developed, areexcellent in terms of impacts on environment and safety of passengers.Such materials, however, have the linear burning velocity of less than30 mm/sec in general. If it is assumed that the linear burning velocityis about 20 mm/sec and that the gas generating material is manufacturedin the form of pellets of 2 mm in diameter or disks of 2 mm thick, whichare advantageous in retaining their shapes, the combustion speed will beabout 100 mm/sec, which fails to meet the desired combustion time of40-60 msec. When the linear burning velocity is approximately 20 mm/sec,to obtain the desired combustion time requires that the material'spellet diameter or disk thickness to be about 1 mm. When the linearburning velocity is less than 10 mm/sec, the gas generating material'sdisk is required to have a thickness of 0.5 mm or less. Thus, it ispractically impossible to manufacture the gas generating material in theform of pellets or disks that are industrially stable and can withstandmany hours of vibrations of an automobile. It has been difficult todevelop the airbag inflator that meets the desired performances.

By way of specific example, reference is made to FIG. 9 wherein aconventional airbag inflator such as disclosed in U.S. Pat. No.4,547,342 of Adams et al., Oct. 15, 1985 is shown.

A housing 40 has a diffuser shell 41 and a closure shell 42. Thediffuser shell 41 is formed by forging and has three concentriccylinders 43, 44, 45 formed integral with a circular portion 46. Likethe diffuser shell 41, the closure shell 42 is also formed by forgingand has three concentric welded portions 50, 51, 52. The diffuser shell41 and the closure shell 42 are joined together at these welded portions50, 51, 52 by friction welding. It is common in the prior art to formthe shells of the airbag inflator by forging.

In this airbag inflator, the cylinder 43 defines an ignition meansaccommodating chamber 53, the cylinder 44 defines a combustion chamber54, and the cylinder 45 defines a coolant/filter chamber 55. Theignition means accommodating chamber 53 accommodates ignition meanscomprising an igniter 56 and a transfer charge 47. In the combustionchamber 54, pellets of a gas generating material 57, ignited by theignition means to produce a gas, and a first coolant/filter 58surrounding the gas generating material 57 to cool the combustion gasand arrest combustion particulates are installed. In the coolant/filterchamber 55, a second coolant/filter 59 to further cool the combustiongas and arrest combustion particulates is installed.

A PROBLEM TO BE SOLVED BY THE INVENTION

Forged products, though they are homogeneous in the metal structure andhighly tenacious, have a drawback of high cost. When the shell membershaving many concentric cylinders as disclosed in the above U.S. patentare manufactured by forging, the circular portion 46 is not flat andrequires a cutting work, which increases the number of manufacturingprocesses and therefore increasing cost. In the shell member having thecylinder 43 formed integral with the circular portion 46 as in the aboveU.S. patent, when the volume of the cylinder 43 is to be changed, theoverall shape of the diffuser shell 41 needs to be changed. Changing thevolume of the cylinder 43, therefore, is not easy. In the aboveconventional airbag inflator, because the coolant/filter chamber isformed outside the combustion chamber, the diameter of the airbaginflator becomes large, increasing its size and weight. Further, becausethe combustion chamber is defined by the cylinder 44 of the diffusershell, the diffuser shell is complex in shape, making the manufacture ofthe airbag inflator difficult, thus increasing the cost.

As a further example, a coolant for an airbag inflator is obtained byrolling a strip-like metal mesh into a multi-layer cylinder. The coolantcools a combustion gas generated in the combustion chamber of the airbaginflator as it passes therethrough and entraps relatively largecombustion particulates. FIG. 12 illustrates an airbag inflator equippedwith a conventional coolant similar to that shown in U.S. Pat. No.4,902,036 to Zander et al., issued Feb. 20, 1990. The airbag inflatorcomprises a housing 231 having gas discharge ports 230, an ignitionmeans accommodating chamber 232 defined at a central portion in thehousing 231, a combustion chamber 233 defined on the outer side of theignition means accommodating chamber 232, and a coolant/filter chamber234 defined on the outer side of the combustion chamber 233. In theignition means accommodating chamber 232, ignition means or an igniter235 and a transfer charge 236 are disposed, and in the combustionchamber 233, a canister 238 filled with a gas generating material 237which is ignited by the ignition means and generates a gas is disposed,and in the coolant/filter chamber 234, a coolant 239 for cooling thecombustion gas generated in the combustion chamber 233 and a filter 240for cleaning the combustion gas are disposed. The combustion chamber 233is defined by a cup-like combustor cup 243, having ports 244 forreleasing the combustion gas, and a center hole 245 formed in the bottomthereof. The coolant/filter chamber 234 is divided by a retainer 242into an upper chamber and a lower chamber. The upper chamber contains afilter 240 and the lower chamber contains a coolant 239.

When a sensor (not shown) detects an impact, a signal is sent to theigniter 235, which is then actuated to ignite the transfer charge 236 toproduce flame of a high temperature and high pressure. The flame passesthrough an opening 241, breaks through the wall of the canister 238 andignites the gas generating material 237 contained therein. Thus, the gasgenerating material 237 burns to generate a gas which gushes through theports 244 formed in the combustor cup 243 and the gas is cooled as itpasses through the coolant 239. Here, relatively large combustionparticulates are entrapped and the remaining combustion particulates areentrapped as the gas further passes through the filter 240. The gas,that is cooled and cleaned, is discharged through the gas dischargeports 230 and flows into an airbag (not shown). Thus, the airbaginflates to form a cushion between a passenger and a hard structure toprotect the passenger from the impact.

The conventional coolant still has a problem from the standpoint ofeffectively entrapping fine combustion particulates because of itssimple clearance structure. Therefore, a filter must be used in additionto the coolant. Moreover, the conventional coolant has a small pressureloss (has a good gas permeability), which makes it difficult to define apressure chamber such as combustion chamber. It is, therefore, necessaryto form a combustion chamber separately from the coolant by using adefining member such as a combustor cup, combustion ring, etc.

Therefore, the airbag inflator, equipped with the conventional coolant,uses an increased number of parts, and has an increased diameterresulting in an increase in the size and weight.

Furthermore, the conventional coolant, having a small bulk density (avalue obtained by dividing a mass of the molded article by a bulk volumethereof), is not capable of defining a pressure chamber, has a smallshape-retaining strength and, hence, deformed upon the application of agas pressure, adversely affecting the entrapping of combustionparticulates.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide an improved andrelatively simplistic airbag inflator structure.

Another object of the present invention is to provide an improved airbaginflator structure utilizing a coolant/filter structure that defines anouter peripheral boundary of a combustion chamber within the inflatorcontaining a gas generating material.

Another object of the present invention is to provide an improved andsimplistic airbag inflator structure that utilizes non-azide gasgenerating materials.

Still another object of the present invention is to provide an improvedand simplistic airbag inflator structure that uses non-azide gasgenerating materials and improved coolant/filter structures that definesan outer periphery of a combustion chamber within said inflatorcontaining said non-azide gas generating materials.

Still another object of the present invention is to provide an improvedand simplistic airbag inflator structure that incorporates an improvedcooperation between the outer housing of the structure and an internalcoolant/filter structure defining an outer periphery of a combustionchamber internal to said outer housing.

Yet another object of the present invention is to provide airbaginflator structures and systems for driver, passenger, and side impactapplications that utilizes the structures, components, and/orpropellants of the present invention.

These and other objects of the present invention will become more fullyapparent with reference to the following specification and drawingswhich are directed to several preferred embodiments, components, andpropellants forming a part of and/or associated with the inflators ofthe present invention.

SUMMARY OF THE INVENTION

A. The Overall Structure

The airbag inflator of this invention comprises: a housing having adiffuser shell and a closure shell, the diffuser shell being formed bypressing a metal plate and having gas discharge ports, the closure shellbeing formed by pressing a metal plate and having a center hole; acentral cylinder member made of a pipe, installed in the housing, anddisposed concentric with the center hole to form an ignition meansaccommodating chamber; and a coolant/filter disposed surrounding thecentral cylinder member to define a combustion chamber for a gasgenerating means and having a pressure loss of 0.3×10⁻² to 1.5×10⁻²kg/cm² at a flow rate of 100 l/min/cm² at a normal temperature, thecoolant/filter being adapted to cool a combustion gas and arrestcombustion particulates; wherein a gas generated in the combustionchamber when an impact occurs is introduced into an airbag to protect apassenger from the impact.

One preferred embodiment of the airbag inflator of this invention thusincludes a diffuser shell, a closure shell, a central cylinder member,and a coolant/filter. These four members are manufactured separately.That is, the diffuser shell and the closure shell are formed by pressinga metal plate; the central cylinder member is made, preferably, byrolling a metal plate into a cylinder and welding its opposing sides;and the coolant/filter is made, preferably, by stacking flat plaitedmetal meshes in a radial direction and compressing them in radial andaxial directions.

By separating, from the diffuser shell, the central cylinder member thathas been formed integral with the circular portion of the diffuser shellin the prior art, the shape of the diffuser shell is simplified. Becauseof this separated forming, the volume of the central cylinder member canbe changed, as required, independently of the diffuser shell. Thecentral cylinder member can be manufactured at low cost by using, forexample, the UO press method. Such a welded pipe can be made by the UOpress method (which involves the steps of forming a plate in a U shape,then forming it into an O shape, and welding the seam) or anelectro-resistance-welding method (which involves the steps of rolling aplate into a cylinder and passing a large current while applying apressure at the seam to weld the seam by resistance heat).

Forming the diffuser shell and the closure shell by pressing makes theirmanufacture easy and reduces their manufacture cost.

The coolant/filter of the airbag inflator is arranged surrounding thecentral cylinder member to define, together with the housing, acombustion chamber for a gas generating means. Further, because of itsrelatively large, predetermined pressure loss, the coolant/filter of theairbag inflator of this invention can arrest combustion contaminants orparticulates contained in the combustion gas with high efficiency.Hence, the filter that has conventionally been provided in addition to acoolant can be obviated.

An alternative embodiment of the inflator structure eliminates thecentral cylinder by use of an ignition canister centrally located in thehousing and mounted on the closure shell within the combustion chamberdefined by the coolant/filter and the housing. The coolant/filter isreferred to herein as a coolant/filter structure or device to betterdescribe its duality of function in cooling and filtering gas generatedby the preferably non-azide gas generating material.

In one preferred embodiment, the pressure loss through thecoolant/filter structure is preferably set at 0.5×10⁻² to 1.2×10⁻²kg/cm² at the flow rate of 100 l/min/cm² at normal temperatures. Morepreferably, it is set at 0.7×10⁻² to 0.9×10⁻² kg/cm² at the flow rate of100 l/min/cm² at normal temperatures.

In the case where an additional mesh layer is provided to strengthen thecoolant/filter, that layer has a pressure loss of at least 1.5×10⁻²kg/cm² under these same conditions.

A suitable solid gas generating means for the airbag inflator includespellets of a gas generating material of NQ/Sr(NO₃)₂/CMC. This is amixture of 32.4% NQ (nitroguanidine) by weight, 57.6% Sr(NO₃ )₂(strontium nitrate) by weight, and 10% CMC (carboxymethyl-cellulose) byweight. NQ functions as a fuel, Sr(NO₃)₂ as an oxidizing agent, and CMCas a binder.

The solid gas generating material preferably has a linear burningvelocity of 5-30 mm/sec under the pressure of 70 kg/cm² and morepreferably 5-15 mm/sec.

The diffuser shell and the closure shell are made of a stainless steelplate 1.2 to 3.0 mm thick. The diffuser shell has the outer diameter of45 to 75 mm and the closure shell 45 to 75 mm. It is preferred that anarrow space of 1.0 to 4.0 mm wide be formed between an outercircumferential wall formed by the diffuser shell and closure shell andthe coolant/filter.

The diffuser shell and the closure shell together form the housing ofthe airbag inflator, and at least one of the shells may be formed with amounting flange. The diffuser shell and the closure shell can be joinedtogether by a variety of welding methods, such as plasma welding,friction welding, projection welding, electron beam welding, laserwelding, and TIG arc welding. As to the material of the diffuser shelland the closure shell, a nickel-plated steel plate may be used insteadof the stainless steel plate. The narrow space between the outercircumferential wall formed by the diffuser shell and closure shell hasa role as a gas passage, through which the gas cooled and cleaned by thecoolant/filter passes to reach the gas discharge ports of the diffusershell.

The gas discharge ports of the diffuser shell may have a diameter of 2.0to 5.0 mm and a total of 12 to 24 such ports may be arranged in thecircumferential direction.

The central cylinder member for an electrically activated inflator isformed of a pipe, which is made by rolling a stainless steel platehaving 1.2 to 3.0 mm thick into a cylinder 17 to 22 mm in outer diameterand welding the opposing sides. In the case of a mechanically-actuatedinflator, the central cylinder plate is 1.5 to 7.5 mm thick with anoutside diameter of 19 to 30 mm.

The central cylinder member preferably has a total of six to ninethrough-holes 1.5 to 3.0 mm across arranged in the circumferentialdirection. These through-holes are arranged in two staggered rows, oneof which may consist, for example, of three through-holes 1.5 mm indiameter and the other may consist of three through-holes 2.5 mm indiameter. The central cylinder member forms a hollow chamber foraccommodating ignition means comprising an igniter and a transfercharge. The through-holes allow flames of the transfer charge to beejected therethrough. The central cylinder member has its innercircumferential portion tapped with a female thread and the igniter isformed with a male thread at its outer circumferential portion. Byscrewing the igniter into the central cylinder member, the ignitionmeans can be securely fixed in the central cylinder member.Alternatively, the central cylinder member may have a swaged portion atone end, which is swaged to fix the ignition means to the centralcylinder member. It can also be secured by welding. The method of fixingthe central cylinder member to the diffuser shell includes frictionwelding, projection welding, laser welding, arc welding, and electronbeam welding.

The coolant/filter is preferably made by stacking the flat-plaited metalmeshes in the radial direction and then compressing them in the radialand axial directions. The coolant/filter thus formed has a complexclearance structure and thus an excellent arresting capability. In thisway, an integrated coolant/filter having both the cooling function andthe arresting function is realized. In a preferred embodiment, such acoolant/filter has a pressure loss of 0.3×10⁻² to 1.5×10⁻² kg/cm² underthe conditions of a normal temperature and a flow rate of 100 l/min/cm².

In more concrete terms, the steps of making the coolant/filter involvesforming a flat-plaited stainless steel mesh into a cylinder,repetitively folding one end portion of the cylinder outwardly to forman annular multi-layer body, and compressing the multi-layer body in adie. Alternatively, the coolant/filter may be made by forming aflat-plaited stainless steel mesh into a cylinder, pressing the cylinderin the radial direction to form a plate member, rolling the plate memberinto a multi-layer cylinder body, and compressing the multi-layercylinder body in a die. The stainless steels that are used for themeshes include SUS304, SUS310S, and SUS316 (JIS Standard). SUS304(18Cr—8Ni—0.06C), an austenite stainless steel, exhibits an excellentcorrosion resistance.

The coolant/filter may also be formed in a double layer structure havinga mesh with a wire diameter of 0.3 to 0.5 mm and, on the inner side ofthe mesh, a layer 1.5 to 2.0 mm thick of a mesh with a wire diameter of0.5 to 0.6 mm. The inner mesh layer has a coolant/filter protectionfunction, i.e., protecting the coolant/filter against the flames fromthe ignition material ejected toward the coolant/filter and against thecombustion gas produced when the gas generating material is ignited andburned by the flames.

The coolant/filter may have an outer diameter of 55 to 65 mm, an innerdiameter of 45 to 55 mm and a height of 26 to 32 mm, namely, thecoolant/filter may have a thickness of 5 to 10 mm. Alternatively, theouter diameter may be 40 to 65 mm, the inner diameter 30 to 55 mm andthe height 19 to 37.6 mm. The coolant/filter preferably has acoolant/filter support member for blocking its displacement. Thecoolant/filter support member has a flame resisting portion that isdisposed facing the flame through-holes formed in the central cylindermember and covers the inner circumferential surface of thecoolant/filter. The flame resisting portion has a coolant/filterprotection function to protect the coolant/filter from the flamesejected toward the coolant/filter, and a combustion facilitatingfunction to change the direction of flame propagation to ensure that theflames from the ignition material reach the entire gas generatingmaterial. The coolant/filter support member may be formed of a stainlesssteel plate or steel plate of 0.5 to 1.0 mm thick.

To prevent entry of external moisture into the housing, the gasdischarge ports of the diffuser shell are preferably closed with analuminum sealing tape having a width of 2 to 3.5 times the diameter ofthe gas discharge ports. Sticking of the aluminum tape can be achievedby using, for example, adhesive aluminum tapes or bonding agents and,more preferably, hot melt adhesives that are melted by heat and canoffer secure bonding.

A cushion for the gas generating material can be installed in thecombustion chamber. The cushion is made of a stainless steel mesh andsecured to an inner surface of the closure shell. The support platepreferably has bent portions at its inner and outer circumferentialportions, whose elasticity securely positions the support plate betweenthe central cylinder member and the coolant/filter. When the cushion isformed of a stainless steel mesh, it can also serve as a coolant. Thecushion can also be formed of a silicon foam body.

The overall height of the housing is preferably in the range of between30 and 35 mm.

The coolant/filter has a predetermined wire diameter and a predeterminedbulk density. The proper setting of the wire diameter and the bulkdensity also make it possible to arrest combustion particulates of theburning gas well and increase the shape retaining strength of thecoolant/filter significantly, thus preventing the coolant/filter frombeing deformed by the gas pressure, assuring the normal function ofarresting combustion contaminant particulates and allowing thecoolant/filter to be reduced in thickness. This bulk density ispreferably from 3.5 to 4.5 g/cm³, but may be from 3.0 to 5.0 g/cm³ witha wire diameter of 0.3 to 0.6 mm.

Instead of a metal mesh, a sintered metal may be used to form thecoolant/filter device. The coolant/filter can also be made from acomposite material of metal and ceramics or from a foamed metal body.

Several other embodiments of the coolant/filter structure are providedand will be more fully described in the detailed description of theinvention in connection with the accompanying drawings.

The present invention also can be utilized in an aluminum housing suchthat as disclosed in U.S. Pat. No. 5,466,420. In this case, the housing,having a thickness of 2-4 mm, is formed by means other than pressforming, and the diffuser shell is connected to the closure shell byfriction welding.

The airbag inflator apparatus of the present invention comprises:

an airbag inflator including:

a housing having a diffuser shell and a closure shell, the diffusershell being formed by pressing a metal plate and having gas dischargeports, the closure shell being formed by pressing a metal plate andhaving a center hole;

a central cylinder member made of a pipe, installed in the housing, anddisposed concentric with the center hole to form an ignition meansaccommodating chamber; and

a coolant/filter made of a metal mesh with a wire diameter of 0.3 to 0.6mm, having a bulk density of 3.0 to 5.0 g/cm³, disposed surrounding thecentral cylinder member to define a combustion chamber for a gasgenerating means and having a pressure loss of 0.3×10⁻² to 1.5×10⁻²kg/cm² at a flow rate of 100 l/min/cm² at a normal temperature, thecoolant/filter being adapted to cool a combustion gas and arrestcombustion particulates;

an impact sensor for detecting an impact and outputting an impactdetection signal;

a control unit for receiving the impact detection signal and outputtinga drive signal to the ignition means of the airbag inflator;

an airbag to be inflated by admitting a gas generated by the airbaginflator; and

a module case for accommodating the airbag.

B. Short Pass Prevention

Another embodiment of the invention provides the ability to form theinflator housing of relatively thin stock by preventing gases fromdistorting the housing and by-passing the end faces of thecoolant/filter as a result of this distortion. The present inventionprovides a combined coolant/filter and cooperative baffle structureprecluding such a short pass or bypass of the coolant/filter, as will bemore fully described in the detailed description of the drawings.Without such preventative structure, unfiltered combustion particulatescan exit the inflator and damage the associated airbag. The structuresprovided are for both driver, passenger, and side impact inflatorconfigurations.

C. Housing Parameters Accommodating Non-azide Propellants

In order to accommodate the relatively slow burning velocities (lessthan 30 mm/sec) of many non-azide propellants, and to insure completecombustion of the gas generating materials in the proper time intervalsfor driver, passenger, and side impact applications, a ratio A/At, whereA is the total surface area of the gas generating material and At is thetotal area of the gas discharge or gas diffuser ports in the diffusershell of the inflator housing is adjusted.

In the case of a driver--side airbag inflator, the preferred amount ofnon-azide propellant is on the order of 20 to 50 g. For passenger-sideapplications, the preferred amount of non-azide propellant is 40 to 120g; and for side impact applications, 10 to 25 g. This combustionparameter is further enhanced by controlling the particulate size of thenon-azide gas generating material as will be more fully describedherein. Other parameters, that are controlled, are the internal volumeof the inflator housing and the quantity of gas generating material,also to be more fully described herein.

Further optimization of gas flow is achieved by controlling the radial(annular) cross-sectional area S_(t) of the defined gas passage or gapbetween the coolant/filter and the housing end walls to be equal to orgreater than the total area A_(t) of the gas discharge or diffuserports. It is preferred that this ratio S_(t)/A_(t) should preferablyfall in the range of 1 to 10 and more preferably 2 to 5.

In order to maintain this annular cross-sectional area of the gaspassage or gap, the coolant/filter is provided with an externalperforated cylindrical reinforcement defining the inner wall of the gaspassage and preventing expansion of the coolant/filter into that passageunder the pressure of the generated gas. Other suitable externalperipheral supporting layers may also be provided for this purpose.

Coolant/filter structures of the present invention control the solidparticulate content of expelled gas from the diffuser ports to less than2 g and preferably from less than 1 g to less than 0.7 g.

Furthermore, the total area At of the diffuser ports/volume of gasproduced is maintained above a desired index and the area At controlledby the size and number of the diffuser ports such that a maximumpressure range of 100 to 300 kg/cm² is maintained within an inflatorhousing having a volume of 130 cc or less, for non-azide gas generatingmaterials whose linear combustion velocity 30 mm/sec or less under apressure of 70 kg/cm². At a housing volume of 120 cc, the total area ofthe gas discharge ports is preferably 1.13 cm².

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of an airbag inflator of the presentinvention;

FIG. 2 is a prospective of a cylindrical metallic mesh used in theprocess of manufacturing a coolant/filter structure of the presentinvention;

FIG. 3 is a schematic illustration of forming the cylindrical mesh ofFIG. 2 into a coolant/filter structure;

FIG. 4 is a cross-sectional schematic of a formed coolant/filterstructure of the present invention;

FIG. 5 is a schematic of a flat plate member formed of metallic meshcylinder pressed in a radial direction;

FIG. 6 is a schematic illustration of a multi-layered mesh cylinderformed by rolling the plate of FIG. 5;

FIG. 7 is a cross-section of another embodiment of the airbag inflatorof the present invention;

FIG. 8 is a schematic of an airbag apparatus of the present inventionincorporating airbag inflators such as those illustrated in FIGS. 1 and2;

FIG. 9 is a cross-section of a conventional airbag inflator;

FIG. 10 is a cross-section of another embodiment of an airbag inflatorof the present invention including a coolant/filter structure of thepresent invention;

FIG. 11 is an illustration of a flat-plaited mesh for the coolant/filterstructure of the present invention;

FIG. 12 is a partial cross-section of a conventional coolant/filterstructure in an airbag inflator;

FIG. 13 is a partial cross-section of another embodiment of thecoolant/filter structure in an airbag inflator of the present invention;

FIGS. 14 and 15 are illustrative embodiments of an outer deformation orswell suppressing component of the coolant/filter structure of FIG. 13;

FIG. 16 is a cross-section of still another embodiment of the airbaginflator of the present invention illustrating additional structuraldetails;

FIG. 17 is a cross-section of yet another embodiment of the presentinvention;

FIG. 18 is a partial cross-section of another embodiment of the airbaginflator of the present invention;

FIG. 19 is a partial cross-section of still another embodiment of theairbag inflator of the present invention;

FIG. 20 is a cross-section of an airbag inflator of the presentinvention adapted for passenger side airbags;

FIG. 21 is a top plan view of the airbag inflator of FIG. 16; and

FIG. 22 is a top plan view of the airbag inflator of FIG. 17.

FIG. 23 is a partial cross-section of still another embodiment of theairbag inflator of the present invention;

FIG. 24 is a cross-section of the airbag inflator of FIG. 23;

FIG. 25 is a cross-section of a mechanical-type sensor of the airbaginflator of FIG. 23;

FIG. 26 is a cross-section of yet another embodiment of the airbaginflator of the present invention;

FIG. 27 is a schematic of a perforated basket of the airbag inflator ofFIG. 26;

FIG. 28 front view of the perforated basket of the airbag inflator ofFIG. 26;

FIG. 29 is a cross-section of still another embodiment of the airbaginflator of the present invention;

FIG. 30 is a schematic of a perforated basket of the airbag inflator ofFIG. 29;

FIG. 31 front view of the perforated basket of the airbag inflator ofFIG. 29;

FIG. 32 is a schematic of an airbag apparatus of the present inventionincorporating an airbag inflator such as those illustrated in FIG. 23;

FIG. 33 is a cross-section of yet another embodiment of the airbaginflator of the present invention;

FIG. 34 is a schematic of a coolant/filter of the airbag inflator ofFIG. 33;

FIG. 35 is a schematic of an airbag apparatus of the present inventionincorporating airbag inflators such as those illustrated in FIG. 20.

FIG. 36 is a cross-section of yet another embodiment of the airbaginflator of the present invention;

FIG. 37 is a schematic of a perforated basket of the airbag inflator ofFIG. 36;

FIG. 38 front view of the perforated basket of the airbag inflator ofFIG. 36;

FIG. 39 is a cross-section of still another embodiment of the airbaginflator of the present invention;

FIG. 40 is a schematic of a perforated basket of the airbag inflator ofFIG. 39;

FIG. 41 front view of the perforated basket of the airbag inflator ofFIG. 39;

FIG. 42 is a cross-section of yet another embodiment of the airbaginflator of the present invention;

FIG. 43 is a schematic of a coolant/filter of the airbag inflator ofFIG. 42.

DETAILED DESCRIPTION OF THE DRAWINGS

A First Preferred Embodiment

FIG. 1 is a cross section of an airbag inflator of the presentinvention. The airbag inflator includes a housing 3 made of a diffusershell 1 and a closure shell 2, a central cylinder member 4 providedinside the housing 3, and a coolant/filter 5 surrounding the centralcylinder member 4.

The diffuser shell 1 is made by pressing a stainless steel plate and itscircumferential wall 6 is formed with 20 gas discharge ports 7, each ofwhich are 3 mm in diameter, arranged at equal intervals in thecircumferential direction. The diffuser shell 1 has an inwardly recessedportion 9 at the center of the circular portion 8. The recessed portion9 holds a transfer charge canister 10 of an ignition device shownbetween the accessed portion and an igniter 18 of the ignition device.The closure shell 2 is made by pressing a stainless steel plate and hasa center hole 12 at the center. Arranged concentric with the center hole12 is the central cylinder member 4, whose end face 34 at the free endside engages with an inner surface 35 of the closure shell. The closureshell 2 also has a mounting flange portion 14 at the free end of acircumferential wall portion 13. The diffuser shell 1 and the closureshell 2 are fitted together at their circumferential wall portions andjoined by a laser weld 15 to form the housing 3.

The central cylinder member 4 is made of a stainless steel pipe withopen ends. One of the open ends is tapped with a female screw 32 and theother of the open ends is fixed to the circular portion 8 of thediffuser shell by inert gas arc welding so that the second end of thecentral cylinder member 4 encloses the recessed portion 9. Inside thecentral cylinder member 4 is formed an ignition device accommodatingchamber 17 for accommodating the ignition device. The ignition devicecomprises an igniter 18 that is activated by a signal from a sensor (notshown), and a transfer charge canister 10 containing a transfer charge(i.e., an ignition-transfer or an enhancer) to be ignited by the igniter18. The outer circumferential surface of the igniter 18 has a male screw36 that engages with the female screw 32 of the central cylinder memberto securely fix the igniter 18 to the central cylinder member 4. Aflange portion 37 of the igniter 18 has a function of preventing thescrews from loosening. The igniter 18 has an O-ring 20 fitted in itsouter circumferential groove, which works as a seal for the ignitiondevice accommodating chamber 17. Near the second end on the diffusershell side, the central cylinder member 4 has two rows of through-holes21 arranged in a staggered relationship. In this embodiment, one of thetwo rows consists of three through-holes 1.5 mm across and the otherconsists of three 2.5 mm diameter holes.

Several preferred construction parameters for the diffuser and closureshells 1 and 2 and the inner cylinder 5 are as follows:

The diffuser shell and the closure shell preferably are made of astainless steel plate 1.2 to 2.0 mm thick and have outer diameters of 65to 70 mm and 65 to 75 mm, respectively. It is also preferred that anarrow space 1.0 to 4.0 mm wide be formed between the outercircumferential wall formed by the diffuser shell and closure shell andthe coolant/filter 5.

The gas discharge ports of the diffuser shell are preferably set to 2.0to 5.0 mm in diameter and a total of 16 to 24 such gas discharge portsarranged in the circumferential direction.

The central cylinder member may be made by rolling a stainless steelplate 1.2 to 3.0 mm thick into a pipe 17 to 20 mm in outer diameter andwelding its seam.

The central cylinder member preferably has a total of six to ninethrough-holes 1.5 to 3.0 mm in diameter arranged in the circumferentialdirection.

These through-holes are preferably arranged in two staggered rows, oneof which consists of three through-holes 1.5 mm in diameter and theother consists of three through-holes 2.5 mm in diameter.

Additionally, the central cylinder 4 is preferably of differentdimensions depending upon the use of electrical or mechanical impactsensors. In a mechanical system, the cylinder wall thickness is 1.5 to7.5 mm with an outside diameter of 19 to 30 mm; and in an electricalsystem, the cylinder wall thickness is 1.2 to 3.0 mm with an outsidediameter of 17 to 22 mm.

The coolant/filter 5 is arranged to surround the central cylinder member4 to define, with the housing 3, a gas generating annular combustionchamber 22 around the central cylinder member 4. The coolant/filter 5 ismade by stacking flat plaited stainless steel meshes in the radialdirection and compressing them in the radial and axial directions, andhas a bulk density of 3.0 to 5.0 g/cm³. A preferred method of formingthe coolant/filter 5 will be described by referring to the drawings.First, stainless steel wires of 0.3 to 0.6 mm in diameter areflat-plaited to form a cylindrical body 60 as shown in FIG. 2. Next, oneend portion 61 of this cylindrical body 60 is folded outwardly as shownin FIG. 3. This folding operation is repeated to form an annularmulti-layer body 62. The number of folding operations is determinedconsidering the wire diameter and the coolant/filter thickness. Finally,this multi-layer body 62 is put in a die (not shown) and compressed inthe radial and axial directions until its bulk density is 3.0 to 5.0g/cm³, thus forming the coolant/filter 5 as shown in FIG. 4.

The coolant/filter of the present invention is obtained by laminatingflat-plaited metal meshes of a wire diameter of 0.3 to 0.6 mm in theradial direction and compressing them in the radial and axialdirections. The coolant/filter obtained by laminating the metal mesheshaving a flat-plait structure in the radial direction and compressingthem, exhibits a complex clearance structure and an excellent entrappingeffect. Therefore, the coolant/filter exhibits an entrapping functionwhich is that of a filter in addition to its cooling function. Accordingto the present invention, therefore, a coolant/filter of the type ofcoolant and filter that are formed integrally together is realizedexhibiting both the cooling function and the entrapping function.

Another method of forming the coolant/filter 5 is explained withreference to FIGS. 5 and 6. After the cylindrical body 60 is formed asshown in FIG. 2, it is compressed in the radial direction to form aplate body 64 as shown in FIG. 5, which is then rolled into a cylinderin multiple layers as shown in FIG. 6 to form a multi-layer body 65.This multi-layer body 65 is compressed in the radial and axialdirections in a die to form the coolant/filter 5.

The coolant/filter 5 formed in this way has its plaited loops in eachlayer collapsed as shown at 63, and the layers of collapsed mesh loopsare stacked in the radial direction. Hence, the clearance structure ofthe coolant/filter is complex, offering an excellent arresting andentrapping capability.

As shown in FIG. 11, the flat plaited mesh can be formed by knittingmetal wire to have loops directed to one direction and a clearancestructure.

Using the above forming method, the compression formed coolant/filter isprovided so that it has a pressure loss of 0.3×10⁻² to 1.5×10⁻² kg/cm²at the flow rate of 100 l/min/cm² at room (normal) temperature.

By inserting another multi-layer body inside the multi-layer body 65 andcompressing them together, a double structure coolant/filter can beobtained. The second multi-layer body may, for example, be made byrolling the plate body 64 of a metal mesh with a wire diameter of 0.5mm, like the one shown in FIG. 5, into a two-layer cylinder as shown inFIG. 6.

This coolant/filter 5 defines the combustion chamber 22 and also has thefunctions of cooling the combustion gas generated in the combustionchamber and arresting combustion particulates. Fitted over the outsideof the coolant/filter 5 is a ring 23, which has a number ofthrough-holes in its entire circumferential wall and reinforces thecoolant/filter 5, all as shown in FIG. 1.

Referring further to FIG. 1, an inclined portion 67 is formed in thecircumferential direction around the circular portion 8 of the diffusershell 1. Similarly, another inclined portion 69 is formed in thecircumferential direction around the annular portion 68 of the closureshell. These inclined portions 67, 69 are designed to block the movementof the coolant/filter 5 and form a space between the circumferentialwalls 6, 13 of the housing and the ring 23 of the coolant/filter 5.

In the combustion chamber 22, pellets of a gas generating material 25and a cushion 26 for the gas generating material 25 are installed. Thering-shaped cushion 26 is made of a stainless steel mesh and secured tothe inner surface 35 of the closure shell 2. The cushion 26 also servesas a coolant. The ring-shaped support plate 24 is made of a stainlesssteel plate and has bent portions 66 at its inner and outercircumferential portions, whose elasticity securely positions thesupport plate 24 between the central cylinder member 4 and thecoolant/filter 5.

Between the circumferential walls 6, 13 of the housing and the ring 23of the coolant/filter is formed a space 28, which serves as a gaspassage, through which the gas, after being cooled and cleaned whilepassing through the coolant/filter 5, is led to the gas discharge ports7 of the diffuser shell. To prevent ambient moisture from entering intothe housing 3, the gas discharge ports 7 of the diffuser shell areclosed by an aluminum sealing tape 29.

In the airbag inflator of the above construction, when a sensor (notshown) detects an impact, its signal is sent to the igniter 18 toactivate it, igniting the transfer charge in the transfer chargecanister 10 to produce hot flames. The flames eject through the rows ofthrough-holes 21 to ignite the gas generating material 25 in thecombustion chamber 22. The gas generating material is burned to producea hot, high-pressure gas, which is then cooled and cleared ofparticulates by the cushion 26 and also cooled and cleared of combustionparticulates while passing through the coolant/filter 5. The combustiongas thus cooled and cleaned passes through the through-holes of theperforated ring 23 and the space 28 and breaks the aluminum sealing tape29 before ejecting through the gas discharge ports 7 and flowing intothe airbag (not shown), which is inflated to form a cushion between thepassenger and surrounding hard structures, thereby protecting thepassenger from impacts.

FIG. 8 shows an airbag apparatus having the airbag inflator of thisinvention. This airbag apparatus comprises an airbag inflator 80, animpact sensor 81, a control unit 82, a module case 83, and an airbag 84.

The airbag inflator 80 employs the airbag inflator explained withreference to FIG. 1.

The impact sensor 81 may, for example, be a semiconductor typeacceleration sensor, which has a silicon substrate beam that deflectswhen an acceleration is applied and four bridge-connected semiconductorstrain gauges formed on the beam. When accelerated, the beam deflects,causing a strain on its surface, which changes resistance of thesemiconductor strain gauges. The resistance change is then detected as avoltage signal proportional to the acceleration.

The control unit 82 has an ignition decision circuit, which receives asignal from the semiconductor type acceleration sensor. When the impactsignal from the sensor exceeds a threshold level, the control unit 82starts calculation. When the calculation result exceeds a predeterminedvalue, the unit sends an activation signal to the igniter 18 of theairbag inflator 80.

The module case 83 is formed of polyurethane, for instance, and includesa module cover 85. The module case 83 accommodates the airbag 84 and theairbag inflator 80, thus forming a pad module, which is mounted to asteering wheel 87 of an automobile.

The airbag 84 is made of nylon (nylon 66 for example) or polyester andis folded and secured to the flange portion 14 of the inflator, with itsinlet 86 enclosing the gas discharge ports 7 of the inflator.

When the semiconductor acceleration sensor 81 detects an impact at timeof automobile collision, the impact signal is sent to the control unit82, which, when the impact signal exceeds the threshold level, startscalculation. When the result of the calculation exceeds a predeterminedvalue, the control unit 82 outputs an activation signal to the igniter18 of the airbag inflator 80. The igniter 18 is thus activated to igniteand burn the gas generating material, producing a gas. The generated gasejects into the airbag 84, which is inflated breaking the module cover85 to form a cushion between the steering wheel 87 and a passenger forabsorbing impacts.

A Second Preferred Embodiment

FIG. 7 shows another embodiment of the airbag inflator of thisinvention. The airbag inflator of this embodiment differs from thatshown in FIG. 1 in terms of the shape of the diffuser shell and closureshell. More specifically, the diffuser shell 1′ and the closure shell 2′have flange portions 30, 31, respectively, which are joined together bywelding. The closure shell 2′ has a bent portion 72, which is made byaxially bending an edge of a center hole and whose inner circumferentialsurface defines a center hole 12′. Further, the diffuser shell 1′ has acircumferentially extending inclined portion 70, which forms a dish-likecircular portion 8′ that helps position a central cylinder member 4′.

The central cylinder member 4′ has one of its ends projecting from theclosure shell 2′, and the projected end is formed with a crimped portion16. The other end of the central cylinder member 4′ is formed with ahorizontally and outwardly projecting flange 33, which is put in contactwith the bottom of the dish-shaped circular portion 8′ of the diffusershell. The central cylinder member 4′ is secured to the diffuser shell1′ by a projection weld between the flange 33 and the circular portion8′. The central cylinder member 4′ has a row of through-holes 21′ nearthe second end on the diffuser shell side. In this embodiment, sixthrough-holes 2.5 mm in diameter are arranged in the circumferentialdirection. The row of the through-holes 21′ is closed by an aluminumsealing tape 74, and a transfer charge 75 is directly loaded in thecentral cylinder member 4′. The central cylinder member 4′ is positionedat the bottom of the dish-shaped circular portion 8′ and fixed to thediffuser shell 1′, after which the center hole 12′ of the closure shellis sleeved over the central cylinder member 4′. Then, the closure shelland the diffuser shell, and the closure shell and the central cylindermember are joined, respectively. A ring-shaped plate member 76 that ismounted to the central cylinder member 4′ by its elastic force works asa welding protection plate. Near the first end on the closure shellside, the central cylinder member 4′ is formed with a stepped portion 71for the igniter 18′. After the transfer charge 75 is loaded, the igniter18′ is also inserted into the central cylinder member 4′ and engageswith the stepped portion 71. Then, the portion 16 of the centralcylinder member is crimped to securely fix the igniter 18′ to thehousing 3′.

The coolant/filter 5′ has a coolant/filter support member 38 that blocksdisplacement of the coolant/filter 5′. The coolant/filter support member38 is made by pressing a stainless steel plate about 1 mm thick and hasan annular portion 39, which surrounds the horizontally and outwardlyprojecting flange 33 and engages with the inclined portion 70, and aflame resisting plate portion 60 bent from the annular portion 39. Theflame resisting plate portion 60 is disposed facing the row ofthrough-holes 21′ which are formed in the central cylinder member forthe passage of flames from the ignition means and covers an innercircumferential surface 61 of the coolant/filter 5. The flame resistingplate portion 60 has a function of protecting the coolant/filter 5′against flames ejected toward it and also a function of changing thedirection of the ejecting flames to ensure that the flames reach the farside of the gas generating material 25′ to facilitate combustion. Inaddition to the inclined portions 67, 69 (FIG. 1) and the coolant/filtersupport member 38, the means for preventing displacement of thecoolant/filter 5′ may also be formed by inwardly projecting both or oneof upper and lower corners 73 of the housing and making the formedprojection engage with the coolant/filter 5′. The perforated ring 23 forthe coolant/filter 5 shown in FIG. 1 is not a must and, in the case ofthe coolant/filter 5′ of the second embodiment, this ring is notprovided.

In the airbag inflator with the above construction, when a sensor (notshown) detects an impact, an impact signal is sent to the igniter 18′,which is then activated to ignite the transfer charge 75 to produce hotflames. The flames break the wall of the aluminum tape 74 and ejectthrough the row of through-holes 21′ into the combustion chamber 22′, inwhich the flames ignite the gas generating material 25′ near thethrough-holes 21′ and are directed by the flame resisting plate portion60 to ignite the gas generating material 25′ at the lower part of thecombustion chamber 22′. As a result, the whole gas generating materialburns, producing a hot, high-temperature gas, which then passes throughthe coolant/filter 5′ and, during such passage, the gas is cooled andcleared of combustion contaminants or particulates. The combustion gasthus cooled and cleaned passes through the space 28′ and the gasdischarge ports 7′ and flows into the airbag (not shown). The airbag isthen inflated to form a cushion between the passenger and surroundinghard structures, thereby protecting the passenger from impacts.

A Third Preferred Embodiment

FIG. 10 illustrates an example where the coolant/filter of the presentinvention is adapted to an airbag inflator for an airbag. The airbaginflator comprises a housing 113 constituted by a diffuser shell 111 anda closure shell 112, a central cylinder member 114 disposed at thecenter in the housing 113, and the coolant/filter 104 arrangedsurrounding the central cylinder member 114.

The diffuser shell 111 is formed by pressing a stainless steel plate andhas a plurality of gas discharge ports 107 formed in the peripheral wall106 thereof maintaining an equal distance in the circumferentialdirection. Due to an inclined portion 170 extending in thecircumferential direction, furthermore, the diffuser shell 111 has adish-like circular portion 108 which works to determine the position ofthe central cylinder member 114. The closure shell 112 is formed bypressing the stainless steel plate and has a hole in the central portionthereof. The edge of the hole is outwardly folded in the axial directionto form a folded portion 172, and a center hole 115 is formed by theinner peripheral surface of the folded portion 172.

The central cylinder member 114 is made of a stainless steel tube withits one end protruding toward the outer side of the closure shell 112and being crimped as designated at 116 at the protruded end. At theother end is formed an outwardly directed flange 133 which is broughtinto contact with the bottom of the dish-shaped circular portion 108 ofthe diffuser shell. The outwardly directed flange 133 and the circularportion 108 are projection-welded together, so that the central cylindermember 114 is secured to the diffuser shell 111. The central cylindermember 114 further has one row of through-holes 121 formed on the sideof the other end thereof.

An ignition device accommodating chamber 117 for containing the ignitiondevice is formed inside the central cylinder member 114. The ignitiondevice comprises an igniter 118 that operates upon receiving a signalfrom the sensor (not shown) and a transfer charge 175 that will beignited by the igniter 118. The row of through-holes 121 are closed byan aluminum sealing tape 174, and the central cylinder member 114 isdirectly filled with the transfer charge 175.

The dish-like circular portion 108 positions on the bottom thereof thecentral cylinder member 114 which is then secured to the diffuser shell111. Thereafter, the central cylinder member 114 is inserted in thecentral hole 115 of the closure shell, and the flange portion 130 of thediffuser shell is placed on the flange portion 131 of the closure shell.Then, the closure shell and the diffuser shell are joined together, andthe closure shell and the central cylinder member are joined together. Aring-like plate member 176, resiliently fitted to the central cylindermember 114, works as a welding protection plate. A step 171 for anigniter 118 is formed at one end of the central cylinder member 114.After being filled with the transfer charge 175, the igniter 118 isinserted in the central cylindrical member 114 and is fitted to the step171. Thereafter, the igniter 118 in the central cylinder member issecured to the housing 113 by crimping portion 116.

The coolant/filter 104 is arranged surrounding the central cylindermember 114 and defines, with the housing 113, an annular chamber or acombustion chamber 122 around the central cylinder member 114. Thecombustion chamber 122 is filled with the pelletized gas generatingmaterial 125. The coolant/filter 104 has a support member 138 forpreventing the movement thereof. The support member 138 is formed bypressing a stainless steel plate, and has an annular portion 139 that isarranged surrounding the outwardly directed flange 133 of the centralcylinder member and that comes into contact with the inclined portion170, and a flame-preventing plate 160 which is folded relative to theannular portion 139. The flame-preventing plate 160 is arranged beingopposed to the row of through-holes 121 and covers the inner peripheralsurface 161 of the coolant/filter 104. The flame-preventing plate 160protects the coolant/filter 104 from the flame that gushes toward thecoolant, and causes the gushing flame to be deflected so that the flamesufficiently reaches the gas generating material.

A space 128 is formed between the coolant/filter 104 and the outerperipheral walls 106, 109 of the housing. The space 128 works as a flowpassage through which the gas that is cooled and cleaned through thecoolant/filter 104 flows to the gas discharge ports 107 of the diffusershell. In order to prevent moisture from infiltrating into the housing113 from the exterior thereof, furthermore, the gas discharge ports 107of the diffuser shell are closed by an aluminum sealing tape 129.

In the thus constituted airbag inflator, when a sensor (not shown)detects a shock, a signal is transmitted to the igniter 118 which thenactuates to ignite the transfer charge 175 to produce flame of a hightemperature. This flame breaks through the aluminum sealing tape 174,gushes through the row of through-holes 121 and enters into thecombustion chamber 122 defined by the coolant/filter 104 and housing113. The flame that has entered into the combustion chamber 122 ignitesthe gas generating material 125 near the row of through-holes 121, isdeflected by the flame-preventing plate 160 and ignites the gasgenerating material 125 in the lower portion of the combustion chamber.Thus, the gas generating material 125 burns to generate a gas of a hightemperature and high pressure. The coolant/filter 104 acts to maintainthe pressure of the combustion gas generated in the combustion chamberat a value desired for the proper combustion of the gas generatingmaterial 125. The combustion gas is cooled by the cooling function ofthe coolant/filter 104 as it passes therethrough. The combustionparticulates contained in the combustion gas are entrapped by thetrapping function of the coolant/filter 104. The combustion gas socooled and cleaned flows through the gas flow passage 128 and entersinto the airbag (not shown) through the gas discharge ports 107. Then,the airbag inflates and forms a cushion between a passenger andsurrounding hard structures to protect the passenger from the impact.

FIG. 13 is a cross-sectional view illustrating, in an enlarged scale, aportion which a coolant/filter, according to another embodiment of thepresent invention, is adapted to the airbag inflator for an airbag, likethat of FIG. 10.

A coolant/filter 104′ is arranged surrounding the gas generatingmaterial 125 and defines an annular chamber or a combustion chamber 122around the central cylinder member 114. The coolant/filter 104′ isobtained by laminating flat-plaited metal meshes of a stainless steel inthe radial direction and compressing them in the radial and axialdirections. The coolant/filter 104′ comprises multiple layers ofcollapsed mesh loops stacked in the radial direction. Thus, the meshclearance structure of the coolant/filter is complex and exhibits anexcellent entrapping effect. On the outer side of the coolant/filter104′, an outer layer 129 comprising laminated metallic mesh members isformed. The outer layer 129 works as a swell suppressing layer forsuppressing the coolant/filter from swelling so that the coolant/filter104′ will not be swollen by the gas pressure when the airbag inflatorhas operated and the space 128 will not be materially narrowed orclosed. The coolant/filter 104′ defines a combustion chamber 122 withthe inflator housing, cools the combustion gas generated in thecombustion chamber, and entraps the combustion particulates. Instead ofhaving an associated outer layer 129, the coolant/filter 104′ may besurrounded by a wire or a belt means. With the wire or the belt meansbeing located at a portion where the two flange portions are joinedtogether, a change in the annular cross-sectional area of space 128 isminimized.

Means for suppressing the coolant/filter from swelling or expanding canbe constituted by using a porous (perforated) cylinder. An example ofsuch a perforated cylinder is shown in FIGS. 14 and 15. The perforatedcylinder has an inner peripheral surface 330, 331 that fits over theouter peripheral surface of the coolant, and has a number ofthrough-holes 334, 335 formed evenly in the whole peripheral wall 332,333. The through-holes 334 are round holes of a small diameter, and thethrough-holes 335 are square holes of a large diameter. The swelling orexpanding suppressing cylindrical layers described above do not affectthe pressure loss of the coolant/filter 104′. They have a pressure lossbeing smaller than the coolant/filter device.

A Fourth Preferred Embodiment

FIG. 16 is a cross section of the airbag inflator of this invention.This airbag inflator includes a housing 403 comprising a diffuser shell401 and a closure shell 402; an ignition device installed in theaccommodation space within the housing 403, i.e., an igniter 404 and atransfer charge 405; a gas generating material to be ignited by theigniter and the transfer charge to produce a combustion gas, i.e., asolid gas generating material 406; a coolant/filter for defining, withthe housing 403, a combustion chamber 428 accommodating the gasgenerating material 406, i.e., a coolant/filter 407; and a space 409formed between the coolant/filter 407 and the outer circumferential wall408 of the housing 403.

The diffuser shell 401 is formed by pressing a stainless steel plate andhas a circular portion 412, a circumferential wall portion 410 formed atthe outer circumference of the circular portion 412, and a flangeportion 419 formed at the free end of the circumferential wall portion410 and extending radially and outwardly. In this embodiment, thecircumferential wall portion 410 is formed with 18 gas discharge ports411, 3 mm in diameter, arranged at equal intervals in thecircumferential direction. The diffuser shell 401 has a raised circularportion 413 projecting outwardly through a step at the central part ofthe circular portion 412. This raised circular portion 413 givesrigidity to the housing, particularly, a ceiling portion and at the sametime increases the volume of the accommodation space. Between the raisedcircular portion 413 and the igniter 404, a transfer charge canister 453containing a transfer charge 405 is held.

The closure shell 402 is formed by pressing a stainless steel plate andhas a circular portion 430, a center hole 415 formed at the center ofthe circular portion 430, a circumferential wall portion 447 formed atthe outer circumference of the circular portion 430, and a flangeportion 420 formed at the free end of the circumferential wall portion447 and extending radially and outwardly. The center hole 415 has anaxial bent portion 414 at its edge. Fitted in the center hole 415 is acentral cylinder member 416, whose end face 417 at one end is flush withan end face 418 of the axial bent portion 414.

The diffuser shell 401 and the closure shell 402 have flange portions419, 420, respectively, which are stacked together and joined by a laserweld 421 to form the housing 403.

The flange portion 419 of the diffuser shell, as shown in FIG. 21, hasmounting portions 410A for mounting the housing 403 on a fitting of apad module. The mounting portions 410A are arranged in thecircumferential direction at 90° intervals and have threaded bolt holes410B. The outline of a flange portion 420 on the closure shell is shownby a dashed line.

The central cylinder member 416 is made of stainless steel with openends and is secured at its other end on the diffuser shell side to theraised circular portion 413 by an electron beam weld 422. Inside thecentral cylinder member 416, an ignition device accommodating chamber423 is formed. Inside the chamber 423, the igniter 404, triggered by asignal from a sensor (not shown), and the transfer charge canister 453,loaded with the transfer charge 405 ignited by the igniter 404, areinstalled. The central cylinder member 416 has an igniter holding member424, which comprises an inward flange portion 425 for restricting theaxial displacement of the igniter 404, a circumferential wall portion426 in which the igniter is fitted and which is fixed inside the innercircumferential surface of the central cylinder member 416, and aportion 427 crimped to axially fix the igniter between it and the inwardflange portion 425. The central cylinder member 416 has through-holes454 near its second end on the diffuser shell side. In this embodiment,six such through-holes 2.5 mm across are arranged at equal intervals inthe circumferential direction.

The central cylinder member 416 is made by rolling a stainless steelplate 1.2 to 2.0 mm thick into a pipe of 17 to 20 mm in outer diameterand welding the seam. Such a welded pipe may be formed by a UO pressingmethod or an electro-resistance-welding method (which involves the stepsof rolling a plate into a cylinder and passing a large current whileapplying a pressure at the seam to weld the seam by resistance heat).

The coolant/filter 407 is disposed surrounding the gas generatingmaterial 406 to define an annular combustion chamber 428 around thecentral cylinder member 416. This coolant/filter 407 is made by stackingflat plaited stainless steel meshes in the radial direction andcompressing them in the radial and axial directions. The coolant/filter467 comprises multiple layers of collapsed mesh loops stacked in theradial direction. Thus, the clearance structure of the coolant/filter iscomplex providing an excellent arresting performance. On the outer sideof the coolant/filter 407 is formed an outer layer 429 made of laminatedmetallic mesh members, which works to prevent the coolant/filter 407from expanding and closing the narrow space 409 by gas pressuregenerated during the operation of the airbag inflator. Thecoolant/filter 407, in addition to defining the combustion chamber 428,also cools the combustion gas produced in the combustion chamber andarrests combustion contaminant particulates. Rather than using the outerlayer 429, it is possible to wind a wire or belt around thecoolant/filter 407. By positioning the wire or belt at the joint of thestacked flange portions, a change in the area of the gas passage in thespace can be minimized.

Means for preventing the coolant/filter 407 from expanding can be formedof a porous (perforated) cylinder member or peripheral layer previouslydescribed with reference to FIGS. 14 and 15.

Referring further to FIG. 16, surrounding the circular portion 430 ofthe closure shell in the circumferential direction is an inclinedportion 431, which works as a displacement prevention means to preventthe displacement of the coolant/filter 407 and also as a means to formthe space 409 between the housing outer circumferential wall 408 and thecoolant/filter 407.

In the combustion chamber 428 are installed a solid gas generatingmaterial 406 and a displacement prevention means for preventing thedisplacement of the coolant/filter 407, i.e., a support member 432 and aplate member 433. The gas generating material 406 is provided in theform of hollow cylindrical pieces. This shape offers an advantage thatthe combustion of the gas generating material 406 occurs in the outerand inner surfaces and thus the overall surface area of the gasgenerating material does not change greatly as the combustion proceeds.The support member 432 comprises a flame resisting plate portion 434,disposed facing through-holes 454 for flames from the ignition deviceand covering the inner circumferential surface of the coolant/filter407, and a circular portion 436 having a center hole 435 in which thecentral cylinder member 416 is fitted. The flame resisting plate portion434 has a coolant/filter protection function to protect thecoolant/filter 407 from the flames ejected toward it, and also acombustion facilitating function to change the direction of flamepropagation by deflection to ensure that the flames of the ignitiondevice reach a sufficient amount of the gas generating material 406. Thecoolant/filter support member 432 has a function of positioning thecoolant/filter during the assembly of the airbag inflator and also worksas a short pass (blow-by) prevention means for blocking a short pass ofcombustion gas between the inner surface 437 of the housing and the endface 438 of the coolant/filter 407 during the operation of the airbaginflator. Such a clearance may be formed by the internal pressure ofcombustion gas acting against the internal walls of the inflatorhousing. The plate member 433 is made of a stainless steel plate of 0.5to 1.0 mm thick, as is the support member 432, and has a center hole 439fitted over the central cylinder member 416, a circular portion 450 incontact with the gas generating material to prevent its displacement,and a circumferential wall portion 451 formed integral with the circularportion 450 and in contact with the inner circumferential surface of thecoolant/filter 407. The plate member 433 is held between the centralcylinder member 416 and the coolant/filter 407 by its elasticity toblock a short pass of combustion gas at the end face of thecoolant/filter on the side opposite the end face 438. The plate member433 also functions as a protection plate during welding.

The space 409 is formed between the outer circumferential wall 408 ofthe housing and the outer layer 429 of the coolant/filter 407 to providea gas passage, annular in radial cross section, around thecoolant/filter 407. In this embodiment, the annular cross-sectional areaof the space in the radial direction is constant. It is also possible toform the coolant/filter in a conical shape so that the radialcross-sectional area of the gas passage increases toward the gasdischarge ports 411. In this case, the radial cross-sectional area ofthe gas passage may take an average value. Instead of the inclinedportion 431, a projection may be provided at the end portion of thecoolant/filter 407 to engage with the outer circumferential wall 408 ofthe housing to prevent displacement of the coolant/filter 407 and toform a space between the outer circumferential wall 408 of the housingand the coolant/filter 407. The area S_(t) of the gas passage in theradial cross section is set larger than the sum A_(t) of open areas S ofthe gas discharge ports 411 in the diffuser shell. The space 409 aroundthe coolant/filter allows the combustion gas to flow through the wholearea of the coolant/filter, thus realizing efficient utilization of thecoolant/filter and effective cooling and cleaning of the combustion gas.The combustion gas thus cooled and cleaned flows through the space 409into the gas discharge ports 411 in the diffuser shell.

To prevent outside moisture from entering into the housing 403, the gasdischarge ports 411 of the diffuser shell are closed with an aluminumsealing tape 452.

In the airbag inflator of the above construction, when a sensor (notshown) detects an impact, an impact detection signal is sent to theigniter 404, which is then activated to ignite the transfer charge 405in the transfer charge canister 453, producing high-temperature flames.The flames eject through the through-holes 454, igniting the gasgenerating material 406 near the through-holes 454, and are directed bythe flame resisting plate portion 434 to ignite the gas generatingmaterial in the lower part of the combustion chamber. As a result, thegas generating material burns to produce high-temperature, high-pressuregas, which passes through the entire area of the coolant/filter 407,during which time the gas is effectively cooled and cleared ofcontaminant particulates. The combustion gas thus cooled and cleanedflows through the space 409, breaks the aluminum sealing tape 452 andejects through the gas discharge ports 411 into the airbag (not shown).The airbag is inflated forming a cushion between the passenger andsurrounding hard structures to protect the passenger from impacts.

The assembly process for the airbag inflator of FIG. 16 consists inputting the diffuser shell 401 joined with the central cylindricalmember 416 so that its raised circular portion 413 is at the bottom,sleeving the plate member 432 over the central cylindrical member 416,fitting the coolant/filter 407 over the outer side of thecircumferential wall of the plate member 432 to position thecoolant/filter 407, filling the solid gas generating material 406 insidethe coolant/filter, and putting the plate member 433 over the gasgenerating material 406. Then, the center hole 415 of the closure shellis put over the central cylindrical member 416 to overlap the flangeportion 420 of the closure shell and the flange portion 419 of thediffuser shell. The overlapping flange portions are laser-welded at 421and 444 to weld together the diffuser shell 401 and the closure shell402, and also the closure shell 402 and the central cylindrical member416. As the final step, the transfer charge canister 453 and the igniter404 are inserted into the central cylindrical member 416 and then anigniter holding member 427 is crimped to securely fix them.

A Fifth Preferred Embodiment

FIG. 17 is a cross section of another embodiment of the airbag inflatoraccording to this invention. The airbag inflator includes a housing 463,preferably having an outer diameter of about 60 mm, comprising adiffuser shell 461 and a closure shell 462; an igniter 464 installedinside the housing 463; a solid gas generating material 466 ignited bythe igniter 464 to produce a combustion gas; a coolant/filter 467 fordefining a combustion chamber 484 accommodating the gas generatingmaterial 466; and a space 469 formed between the coolant/filter 467 andan outer circumferential wall 468 of the housing 463.

The diffuser shell 461 is made by pressing a stainless steel plate andhas a circular portion 478 and a circumferential wall portion 476 formedat the outer circumference of the circular portion 478. Thecircumferential wall portion 476 has a plurality of gas discharge ports477 arranged at equal intervals in the circumferential direction. Thediffuser shell 461 has a plurality of radial ribs 479 in the circularportion 478. These radial ribs 479 give rigidity to the circular portion478 of the diffuser shell so that the circular portion 478 forming theceiling of the housing will not deform by the gas pressure.

As also shown in FIG. 22, these radial ribs 479 give rigidity to thecircular portion 478 of the diffuser shell so that the circular portion478 forming the ceiling of the housing will not deform by the gaspressure. The flange portion of the diffuser shell, as shown in FIG. 22,has mounting portions 476A to be mounted on a fitting of a pad module.The mounting portions 476A are arranged at 90° intervals in thecircumferential direction and have threaded bolt holes 476B.

The closure shell 462 is made by pressing a stainless steel plate andhas a circular portion 471 and a circumferential wall portion 472 formedat the outer circumference of the circular portion 471. The circularportion 471 has a recessed portion 473 at the central part, which inturn has a center hole 474 at the center. The center hole 474 has anaxial bent portion 475 at its edge, which has an inner circumferentialsurface 481, in which a body portion 480 of the igniter 464 is fitted,and an end face 483 with which a flange portion 482 of the igniter 464engages. The inner circumferential surface 481 of the axial bent portion475 provides a relatively large seal surface. To secure air tightness, asealing material may be applied between the body portion 480 of theigniter 464 and the inner circumferential surface 481, or welding may beapplied between the flange portion 482 of the igniter and the end face483. The end face 483, with which the flange portion 482 of the igniter464 engages, serves to prevent the igniter 464 from coming off by thegas pressure in the combustion chamber 484. The recessed portion 473gives rigidity to the circular portion 471 of the closure shell andkeeps a connector bottom surface 485 of the igniter 464 recessedinwardly from the outer surface of the circular portion 471.

The diffuser shell 461 has a flange portion 486 extending radially andoutwardly at the free end of the circumferential wall portion 476. Theclosure shell 462, too, has a flange portion 487 extending radially andoutwardly at the free end of the circumferential wall portion 472. Theseflange portions 486, 487 are stacked together at an axially centralposition of the housing and welded by laser welding at 488 to join thediffuser shell 461 and the closure shell 462. These flange portions 486,487 give rigidity to the outer circumferential wall of the housing toprevent deformation of the housing due to gas pressure.

The igniter 464 is a commonly used electric igniter that is activated bya signal from a sensor (not shown). The electric igniter does notinclude a mechanical structure and is simple in construction, small insize and light in weight, and is thus preferable to the mechanicaligniter. This igniter 464 (output: 300 to 1500 psi in a 10 cc airtightpressure vessel) does not include a transfer charge canister 453 of FIG.16 or the like. This is because the gas generating material 466 hasexcellent ignition and burning characteristics. That is, this gasgenerating material 466 has a decomposition ignition temperature of 330°C. or less and a combustion temperature of 2000° K or higher. The gasgenerating material 466 is formed into hollow cylindrical pieces and,because of this shape, combustion occurs both at the outer surface andinner surface, offering the advantage that the overall surface area ofthe gas generating material does not change greatly as combustionproceeds.

The coolant/filter 467 is disposed concentric with the center hole 474,and, together with the housing 463, forms the combustion chamber 484.The coolant/filter 467 is formed by stacking flat plaited stainlesssteel meshes in the radial direction and compressing them in the radialand axial directions. The coolant/filter 467, in addition to definingthe combustion chamber 484, also cools the combustion gas produced inthe combustion chamber and arrests combustion particulates. On the outerside of the coolant/filter 467 is formed an outer layer 489 made oflaminated metallic mesh, which reinforces the coolant/filter andprecludes swelling thereof.

Surrounding the circular portion 471 of the enclosure shell andextending in the circumferential direction is an inclined portion 490,which functions as means for positioning the coolant/filter 467 andpreventing its displacement. It also works as means for forming thespace 469 between the outer circumferential wall 468 of the housing andthe outer layer 489 of the coolant/filter.

In the combustion chamber 484 there are installed the solid gasgenerating material 466 and the plate member 491. The gas generatingmaterial 466 is directly filled within the space inside the combustionchamber and disposed adjacent to the igniter 464. The displacement ofthe gas generating material 466 is prevented by a circular portion 492of a plate member 491 that closes any opening between one end of thecoolant/filter 467 and the shell portion 478. The plate member 491 hasthe circular portion 492 and a circumferential wall portion 493 formedintegral with the circular portion 492, which engages with and coversthe inner circumferential surface of one end portion of thecoolant/filter 467. This plate member 491 blocks the combustion. gasform passing between an end face 494 at one end of the coolant/filterand the inner surface of the diffuser shell circular portion 478 (shortpass). When the plate member 491 that blocks the short pass is provided,the fixing of the coolant/filter to the housing is needed only at theend face 495 on the opposite side.

Between the outer circumferential wall 468 of the housing and the outerlayer 489 of the coolant/filter 467 is formed a narrow space 409, whichprovides a gas passage 409′, annular in a radial cross section, aroundthe coolant/filter 467. As with the airbag inflator shown in FIG. 16,the area of the space 409 in the annular radial cross section is setlarger than the total open areas of the gas discharge ports 477 in thediffuser shell. The spacer 469, provided around the coolant/filter,ensures that the combustion gas passes through the entire area of thecoolant/filter 467 and flows toward the gas passage 409′, therebyenhancing uniformity of flow and realizing an efficient use of thecoolant/filter 467 and effective cooling and cleaning of the combustiongas. The combustion gas cooled and cleaned in this manner passes throughthe space 409 to reach the gas discharge ports 477 in the diffusershell. To prevent entry of outer moisture into the housing 463, the gasdischarge ports 477 in the diffuser shell are sealed from inside with analuminum sealing tape 496.

The airbag inflator is assembled in the following procedure. First, theclosure shell 462 is placed such that its circular portion 471 is at thebottom and the igniter 464 is installed in the center hole 474. Next,the coolant/filter 467 is installed and the solid gas generatingmaterial 466 is filled inside the filter. Then the plate member 491 isfitted over the gas generating material 466. Finally, the flange portion486 of the diffuser shell is stacked on the flange portion 487 of theclosure shell and they are welded by the laser weld 488 to join thediffuser shell 461 and the closure shell 462.

In the airbag inflator of this construction, when a sensor (not shown)detects an impact, an impact detection signal is sent to the igniter464, which is activated to ignite the gas generating material 466 in thecombustion chamber 484. The gas generating material burns and produces ahigh-temperature, high-pressure gas, which enters the entire area of thecoolant/filter 467, and during the passage through the coolant/filter467, is cooled and cleared of combustion contaminant particulates. Thecombustion gas, cooled and cleaned in this way, passes through thenarrow space 409, breaks the aluminum sealing tape 496, and flowsthrough the gas discharge ports 477 into the airbag (not shown). Theairbag then inflates forming a cushion between a passenger and a hardstructure, protecting the passenger from impacts.

In the foregoing embodiments shown in FIGS. 16 and 17, the diffusershell and the closure shell together form a housing for the airbaginflator and are made from a stainless steel plate preferably 1.2-3.0 mmthick and 45-75 mm, or more preferably 50-70 mm, in outer diameter. Thediffuser shell and the closure shell can be joined by a variety ofwelding methods, such as electron beam welding, laser welding, TIG arcwelding, and projection welding. Instead of the stainless steel plate, anickel-plated steel plate may be used as the material of the diffusershell and closure shell. The gas discharge ports of the diffuser shellmay have a diameter of 1.5-4.5 mm and a total of 16 to 24 such ports maybe arranged in the circumferential direction. The overall height of thehousing (from the top surface of the diffuser shell to the bottomsurface of the closure shell) is preferably set to 25-40 mm.

A Sixth Preferred Embodiment

FIG. 18 shows another example of an airbag inflator, which is similar tothe one shown in FIG. 16 and in which a diffuser shell 401′ and aclosure shell 402′ are formed by casting aluminum alloy. The diffusershell 401′ has a circular portion 412′, a central cylinder portion 416′formed integral with the circular portion 412′, a circumferential wallportion 410′ formed at the outer circumference of the circular portion412′, and a flange portion 419′ formed at the free end of thecircumferential wall portion 410′ and extending radially and outwardly.The closure shell 402′ has a circular portion 430′, a center hole 415′formed at the center of the circular portion 430′, a circumferentialwall portion 447′ formed at the outer circumference of the circularportion 430′, and a flange portion 420′ formed at the free end of thecircumferential wall portion 447′ and extending radially and outwardly.The center hole 415′ is fitted over the outer circumference of thecentral cylinder portion 416′; the flange portion 419′ of the diffusershell and the flange portion 420′ of the closure shell are stacked andlaser-welded at 421′ to join the diffuser shell and the closure shell toform the housing 403′. Similar to the inflator as illustrated in FIG.16, the inflator of the present embodiment also includes a combustionchamber 428′, having a coolant/filter 407′ therein, and an ignitiondevice accommodating chamber 423′ defined by a central cylinder member416′ protruding from the diffuser shell 401′. A narrow space 409′ isprovided between the coolant/filter 407′ and the housing. The membersidentical with those of FIG. 16 are given like reference numbers andtheir descriptions are omitted.

In the airbag inflator, as illustrated in FIG. 18, the closure shell islaser-welded to the diffuser shell to form the housing. However,friction welding can also be used instead of the laser welding asdisclosed in U.S. Pat. No. 5,466,420.

A Seventh Preferred Embodiment

FIG. 19 shows another example of an airbag inflator, which is similar tothe one shown in FIG. 17 and in which a diffuser shell 461′ and aclosure shell 462′ are formed by casting aluminum alloy. The diffusershell 461′ has a circular portion 478′, a circumferential wall portion476′ formed at the outer circumference of the circular portion 478′, anda flange portion 486′ formed at the free end of the circumferential wallportion 476′ and extending radially and outwardly. The closure shell462′ has a circular portion 471′, a circumferential wall portion 472′formed at the outer circumference of the circular portion 471′, and aflange portion 487′ formed at the free end of the circumferential wallportion 472′ and extending radially outwardly. At the center of thecircular portion 471′ is formed a center hole 474′, in which a bodyportion 480 of the igniter 464 is fitted. The flange portion 482 of theigniter 464 engages with the inner surface 497 of the circular portion471′ of the closure shell. The flange portion 486′ of the diffuser shelland the flange portion 487′ of the closure shell are overlapped andlaser-welded at 488′ to join the diffuser shell 461′ and the closureshell 462′ to form the housing 463′. The members identical with those ofFIG. 17 are given like reference numbers and their explanations areomitted.

An Eighth Preferred Embodiment

FIG. 20 is a cross section of an airbag inflator of this inventionsuited for an airbag apparatus used for the front passenger seat. Theairbag inflator of FIG. 20 has a housing 504, which includes acylindrical portion 501 formed with a plurality of gas discharge ports500 arranged in circumferential and axial directions and sidewallportions 502, 503 provided at the ends of the cylindrical portion 501.At the center in the housing 504 is arranged a transfer charge tube 505,over which are sleeved a number of disk-shaped pieces of a gasgenerating material 506. Surrounding these is a coolant/filter 507. Inone of the sidewall portions 502 is installed an ignition devicecomprising a transfer charge 508 and an igniter 509. The ignition deviceis accommodated in the transfer charge tube 505. A fixing bolt 510 issecured to the other sidewall portion 503. The transfer charge tube 505has many openings 511, through which flames of the transfer charge 508eject and which are distributed evenly over the wall of the transfercharge tube. In at least an area where the gas discharge ports 500 areformed, the inner surface of the housing 504 is bonded with an aluminumsealing tape 524. This aluminum sealing tape 524 hermetically closes thegas discharge ports 500 to prevent external moisture from entering intothe housing through the gas discharge ports 500.

A plate member 512 is installed at the right end of the coolant/filter507 and a plate member 513 at the left end. The plate member 512comprises a circular portion 515, which closes a right end opening 514of the coolant/filter 507, and a circumferential wall portion 517 formedintegral with the circular portion 515 and engaging with an innercircumferential surface 516 of the coolant/filter. The circular portion515 has a center hole 518 that is fitted over the outer circumferentialsurface of the transfer charge tube 505. The plate member 513, like theplate member 512, has a circular portion 521, a circumferential wallportion 522, and a center hole 523. These plate members 512, 513,because they are blocked from moving in the radial direction by thetransfer charge tube 505, function as means for positioning thecoolant/filter 507 during the assembly of the airbag inflator. Further,the plate members 512, 513 work as means for preventing the displacementof the coolant/filter 507 due to vibration of the vehicle and also as ashort pass prevention means for preventing a short pass of thecombustion gas between the inner surface 519 of the housing and thecoolant/filter end face 520 during the operation of the airbag inflator.

The space 525 is formed between the cylindrical portion 501 of thehousing and the coolant/filter 507 to provide a gas passage, annular inradial cross section, around the coolant/filter 507. The area S_(t) ofthe gas passage in the radial annular cross section is set larger thanthe sum A_(t) of open areas S of the gas discharge ports 500 in thecylindrical portion. The space 525 around the coolant/filter allows thecombustion gas to flow through the entire area of the coolant/filtertoward the gas discharge ports 500, thus realizing enhanced uniformityof flow and efficient utilization of the coolant/filter and effectivecooling and cleaning of the combustion gas. The combustion gas thuscooled and cleaned flows through the gas passage into the gas dischargeports 500 in the cylindrical portion.

When a sensor detects an impact, an impact detection signal is sent tothe igniter 509, which is then activated to ignite the transfer charge508, producing high-temperature flames. The flames eject through theopenings 511 of the transfer charge tube 505, igniting the gasgenerating material 506 near the openings. As a result, the gasgenerating material 506 burns to produce high-temperature, high-pressuregas, which passes through the entire area of the coolant/filter 507,during which time the gas is effectively cooled and cleared ofcontaminant particulates. The combustion gas thus cooled and cleanedflows through the space 525, breaks the aluminum sealing tape 524, andejects through the gas discharge ports 500 into the airbag (not shown).The airbag is inflated forming a cushion between a passenger andsurrounding hard structures to protect the passenger from impacts.

In the airbag inflator shown in FIGS. 16 and 17, for example, the ratiobetween the total surface area A of the cylindrical pieces of solid gasgenerating material 406 and the total surface area At of open areas ofthe gas discharge ports 411 in the diffuser shell is set to A/At=100-300with 20 to 50 g of gas generating material. This setting of the surfacearea ratio adjusts the combustion speed of the gas generating materialto a value appropriate for the airbag at the driver's seat and ensuresthat the gas generating material in the airbag inflator burns completelywithin a desired duration.

In the airbag inflator shown in FIG. 20, for example, the ratio betweenthe total surface area A of the cylindrical pieces of solid gasgenerating material 506 and the total surface area At of open areas ofthe gas discharge ports 500 in the cylindrical portion is set toA/At=80-240 with 40 to 120 g of gas generating material. This setting ofthe surface area ratio adjusts the combustion speed of the gasgenerating material to a value appropriate for the airbag at the frontpassenger seat and ensures that the gas generating material in theairbag inflator burns completely within a desired duration. By contrast,a suitable ratio for a side-impact airbag inflator, albeit of similarstructure, is 250-3600 with 10 to 25 g of gas generating material.

FIG. 35 shows an airbag apparatus suitable for use in a passenger side.The airbag apparatus of the present invention has an inflator 80″,suitable for a passenger side airbag apparatus, an airbag 84″, both ofwhich are disposed inside a module case 83″. Further, a shock sensor 81″is connected to the inflator 80″ through a control unit 82″. Thepassenger side airbag apparatus, as shown in FIG. 35, is disposed in apassenger side dashboard, for example, of a vehicle.

The inflator 80″ of FIG. 35, which shows one of the preferredembodiments of the present invention, is an electrically activatedinflator, as previously described with respect to FIG. 20. However, amechanically-activated inflator having a mechanical shock sensor canalso be used as long as the inflator has a housing, which is elongatedalong a central axis thereof, and gas exhaust ports in periphery andaxial directions of the housing.

The airbag 84″ is made of nylon (i.e., nylon 66), or polyester, and hassufficient capacity to maintain safety of a passenger. The airbag isattached to an opening of the module case 83″, folded, and installedinside the module case 83″.

The module case 83″, made of polyurethene, for example, has a sizesufficient to install the inflator 80″ and the airbag 84″. A pad moduleis constituted by installing the airbag 84″ and the inflator 80″ in themodule case 83″. The pad module is disposed, for example, in thepassenger side dashboard.

The shock sensor 81″ and the control unit 82″ are identical to thesensor and unit used in the airbag apparatus as described with respectto FIG. 8.

In this airbag apparatus, the control unit 82″ initiates a calculationwhen it receives a signal, from the shock sensor 81″, generated by ashock due to a collision of the vehicle. The inflator 80″ is activatedand generates combustion gas based on a result of calculation. The gasgenerated by the inflator 80″ flows into the airbag 84″. Thus, theairbag 84″ expands outside the module case 83″ and forms a cushion,which absorbs the shock, between the passenger and the dashboard.

A Ninth Preferred Embodiment

FIG. 23 shows a mechanically actuated inflator which uses a mechanicalsensor for detecting a shock. The mechanically actuated inflator, asshown in FIG. 23, is particularly suitable when installed in a driverside.

The mechanically actuated inflator, as illustrated in FIG. 23, has ahousing which includes a diffuser shell 1501 having a plurality of gasdiffuser ports 1511 at a periphery thereof, and a closure shell 1502,having a central opening 1513, joined to the diffuser shell 1501. Bothshells can be joined together by various welding methods such as plasmawelding, friction welding, projection welding, electron beam welding,laser welding, and TIG arc welding. The housing has two chamberstherein, defined by a cylindrical separation wall 1503 disposedconcentrically with the central opening 1513. The separation wall 1503defines an ignition device accommodating chamber 1504 and a combustionchamber 1505. As stated in the description with respect to FIGS. 1, 7,10, 16, for example, gas generating propellants 1506, a coolant/filter1507, a coolant/filter supporting element 1509, a ring 1510, aring-shaped plate member 1512, and other elements suitable for theactuation of the inflator are installed inside the combustion chamber1505. Also, it is possible to provide, for example, a space 1514 outsidethe coolant/filter 1507.

In the inflator, as illustrated in FIG. 24, an ignition device forigniting the propellants includes: a mechanical-type sensor 1550, whichmechanically detects a shock and fires a firing pin 1551; a detonator1515, which is ignited and burnt by being pierced by the firing pin 1551fired from the mechanical-type sensor 1550; and a transfer charge 1508which burns the propellants 1506 by being ignited and burnt by the flamefrom the ignited detonator 1515. The ignition device, shown in FIG. 24,is disposed inside the ignition device accommodating chamber 1504 of thehousing. A detonator piece 1516 for accommodating and fixing thedetonator 1515 is disposed between the transfer charge 1508 and themechanical-type sensor 1550. The detonator piece 1516 is attached to theseparation wall 1503 by disposing the detonator 1515 at the centralaxial of the housing. The mechanical-type sensor 1550 is disposed insidethe chamber 1504 such that the firing pin 1551, which is fired when thesensor 1550 detects a shock, can pierce the detonator 1515. Thedetonator piece 1516 includes a penetration port 1517 which connects aportion where the detonator 1515 is installed and a portion where thetransfer charge 1508 is installed. In order to avoid the detonator 1515from adsorbing moisture, a sealing tape (not shown) can be attached oneither one or both ends of the penetration port 1517 to block the port1517.

For the mechanical-type sensor 1550, which mechanically detects a shockand fires the firing pin 1551, a sensor, as illustrated in FIG. 25,constructed by: urging a single firing pin 1551 against a cam face 1554of a trigger 1553 by a coil spring 1552; forming a depression 1555adjacent the cam face 1554 such that an engagement of the trigger 1553and the firing pin 1551 is released; and providing a ball 1557 in acylinder 1556 and engaging the ball 1557 with an arm portion 1560 of aholder 1559 which is upwardly urged by a coil spring 1558, can be used.When a shock is applied to this mechanical-type sensor 1550, the ball1557 moves in a downward direction inside the cylinder 1556, therebymoving the holder 1559 downward via the arm portion 1560. The movementof the holder 1559 rotates the trigger 1553, and disengages the cam faceof the trigger 1553 from the firing pin 1551. This causes the coilspring 1552 to project the firing pin 1551 through the depression 1555and hit the detonator 1515. The structure of this mechanical-type sensor1550 is simple and the capacity and weight thereof is less as comparedto a mechanical-type sensor having two firing pins, since this sensor1550 utilizes only one piercing mechanism for the firing pin.

FIG. 32 shows an airbag apparatus having a mechanically-actuatedinflator 380′. The airbag apparatus shown in the figure includes themechanically-actuated inflator 380′, as illustrated in FIG. 23, and anairbag 384′ installed inside a module case 383′.

The module case 383′ is made, for example, of a polyurethane andincludes a module cover 385′. The airbag 384′ and the inflator 380′ aredisposed inside the module case 383′ to form a pad module. The padmodule is attached to a steering wheel 387′ of an automobile.

The airbag 384′ is made of nylon (i.e., nylon 66), or polyester. The gasexhaust ports 307′ of the inflator 380′ are surrounded by an opening ofthe airbag 384′, and the airbag is folded and attached to a flangeportion 314′ of the inflator.

In the airbag apparatus utilizing a mechanically-activated inflator380′, as described above, a shock sensor for detecting a shock and acontrol unit for managing an operation of the inflator, which arerequired in an electrically activated inflator, as illustrated in FIG.8, and harnesses for connecting these elements are not necessary.

This airbag apparatus activates the inflator 380′ and spouts combustiongas from the gas exhaust port 307′ by detecting a shock, generated by acollision of the vehicle, by a mechanical-type sensor 381′. The gasflows into the airbag 384′ and expands the bag. The bag, then, tears themodule cover 385′ and forms a cushion between the steering wheel 387′and a passenger.

A Tenth Preferred Embodiment

FIG. 26 shows an inflator for an airbag having a perforated basket 2650,made of stainless steel, aluminum, or carbon steel, between gasgenerating propellants 2606 and a coolant/filter 2607. The inflator hasa housing which includes a diffuser shell 2601 having a plurality of gasdiffuser ports 2611 and a closure shell 2602, which is joined to thediffuser shell 2601 by one of various welding methods. The housing hastwo chambers therein, defined by an approximately cylindrical separationwall 2603 disposed concentrically with a central opening 2613. Theseparation wall 2603 defines an ignition device accommodating chamber2604 and a combustion chamber 2605. An ignition device including, forexample, a transfer charge 2608 and a mechanical-type sensor 2612, asdescribed in conjunction with FIGS. 23-25, is disposed inside theignition device accommodating chamber 2604. A perforated basket 2650, asshown in FIGS. 27 and 28, and gas generating propellants 2606, acoolant/filter 2607, a coolant/filter supporting element 2609, a ring2610, a ring-shaped plate member 2616, and other elements suitable forthe actuation of the inflator are installed in the combustion chamber2605. Also, it is possible to provide, for example, a space 2614 outsidethe coolant/filter 2607.

The perforated basket 2650 is approximately cylindrical in shape and hasa plurality of through-holes 2651 on the peripheral wall surface 2652 inperipheral and axial directions. The through-holes 2651 can be eitherformed at a predetermined interval with regularity or randomly. Further,the size of the through-holes 2651 can be freely adjusted within therange that does not affect the flow of the combustion gas passingtherethrough. The perforated basket 2650 is disposed between the gasgenerating propellants 2606 and the coolant/filter 2607, and covers theentire area where the coolant/filter 2607 is exposed. In other words,the entire area below a flame resisting plate portion 2615 of thecoolant/filter supporting element 2609. The flame resisting plateportion 2615 has a height of 8-15 mm and extends at least 2 mm below thelowest through-holes in the separation wall, for example, and preventsflames from the through-holes in the separation wall from contacting thecoolant/filter 2607. Further, the perforated basket 2650 can be designedto have the same or slightly shorter axial length than that of thecoolant/filter 2607 such that the perforated basket 2650 extends to theoutside of the flame resisting plate portion 2615 of the coolant/filtersupporting element 2609, thereby overlapping with the flame resistingplate portion 2615.

FIG. 27 shows a perforated basket 2650 provided inside themechanically-actuated inflator having the mechanical-type sensor 2612.However, the perforated basket 2650 can also be used in electricallyactuated inflators as shown in FIGS. 1, 7, 10, 16, 17, and 19.

An Eleventh Preferred Embodiment

Similar to the airbag inflator shown in FIG. 26, FIG. 29 shows aninflator for an airbag having a housing which includes a diffuser shell601′, having a plurality of gas diffusion ports 611′, and a closureshell 602′ joined to the diffuser shell 601′. The closure shell 602′ hasa central opening 613′. The housing has a separation wall 603′ whichdefines the housing into two chambers, namely, an ignition deviceaccommodating chamber 604′ and a combustion chamber 605′. An ignitiondevice, including a transfer charge 608′ and a mechanical-type sensor612′, as described in conjunction with FIG. 23, is disposed inside theignition device accommodating chamber 604′. In addition to a perforatedbasket 650′, as shown in FIGS. 30 and 31, gas generating propellants606′, a coolant/filter 607′, a ring 610′, a ring shaped plate member609′, and other elements suitable for the actuation of the inflator areinstalled in the combustion chamber 605′. Also, it is possible toprovide, for example, a space 614′ outside the coolant/filter 607′. Theperforated basket 650′ is made of stainless steel, aluminum, or carbonsteel.

In the present embodiment, the perforated basket 650′ disposed betweenthe gas generating propellants 606′ and the coolant/filter 607,′ has ashape different from the perforated basket 2650 shown in FIG. 26. Asillustrated in FIGS. 30 and 31, the perforated basket 650′ includes aperipheral wall 652′ having a plurality of through-holes 651′, and anapproximately flat circular cap portion 653′ formed at the upper openingof the peripheral wall 652′. The cap portion 653′ may be formed suchthat it engages with an inner surface of an upper circular portion 616′of the housing. Since this particular embodiment has a cylindricalseparation wall 603′ attached to the diffuser shell 601′, for definingthe ignition device accommodating chamber 604′, the cap portion 653′ ofthe perforated basket 650′ has an opening 654′ at the center portionthereof, for inserting the separation wall 603′.

In the perforated basket 650′ of the present embodiment, thethrough-holes 651′ are formed at portions of the peripheral wall 652′other than portions where it radially opposes the through-holes 617′ inthe separation wall 603′. In other words, the basket 650′ can protectthe coolant/filter 607′ from flames spouting from the through-holes 617′due to the combustion of the transfer charge 608′. Further, to deflectthe flames such that the flames sufficiently reach the gas generatingpropellants 606′, the through-holes 651′ in the peripheral wall 652′ ofthe perforated basket 650′ are formed at portions other than where itwould be exposed to the flames from the through-holes 617′ of theseparation wall 603′. Preferably, the through-holes 651′ are formed, atregular intervals, at portions of the periphery wall 652′ at least 2 mmbelow the flame spouting portions of the separation wall 603′. As aresult, the upper portion of the perforated basket 650′, morespecifically, the portion above the through-holes 651′, has acoolant/filter protecting function which protects the coolant/filter607′ from the flames of the transfer charge 608′ spouting toward thecoolant/filter 607′, and also a combustion enhancing function whichdeflects the flames such that the flames sufficiently reach the gasgenerating propellants 606′. As in the case of the perforated basket asillustrated in FIGS. 26-28, the size of the through-holes 651′ can beadjusted in the similar manner.

FIG. 29 shows a perforated basket 650′ provided inside themechanically-actuated inflator having the mechanical-type sensor 612′.However, the perforated basket 650′ can also be used in electricallyactuated inflators as shown in FIGS. 1, 7, 10, 16, 17, and 19.

A Twelfth Preferred Embodiment

The airbag inflator, as illustrated in FIG. 33, is characterized in thatthe coolant/filter 750 consisting of two or more layers, is installed ina housing. The housing has a separation wall 703 which defines thehousing into two chambers, namely, an ignition device accommodatingchamber 704 and a combustion chamber 705. An ignition device, includinga transfer charge 708 and a mechanical-type sensor 715, as described inconjunction with FIG. 23, is disposed inside the ignition deviceaccommodating chamber 704. In addition to a coolant/filter 750 havingtwo or more layers, as illustrated in FIG. 34, gas generatingpropellants 706, a coolant/filter supporting element 709, a ring 710, aplate member 712, and other elements suitable for the actuation of theinflator are installed in the combustion chamber 705. Also, it ispossible to provide, for example, a space 714 outside the coolant/filter750.

The coolant/filter 750, consisting of two or more layers, can beconstructed by forming an inner layer 751 and an outer layer 752 withdifferent densities or different materials, and superimposing these in aradial direction. When constructing a coolant/filter 750 with layershaving different densities, the inner layer 751 can be formed with acoarse metal mesh and the outer layer 752 can be formed with a finemetal mesh. For the coarse metal mesh used in the inner layer 751, anannular metal mesh layer, which is compressed in a mold, can be used.

In the present embodiment, as illustrated in FIG. 33, a coolant/filterstructure as described in the foregoing, was installed in themechanically-actuated inflator having the mechanical-type sensor 715.However, such coolant/filter can also be installed in electricallyactuated inflators as shown in FIGS. 1, 7, 10, 16, 17, and 19.

A Thirteenth Preferred Embodiment

The airbag inflator of the present embodiment, as illustrated in FIG.36, is similar to the airbag inflator as illustrated in FIG. 26. Theinflator of the present embodiment has a perforated basket 850, asillustrated in FIGS. 37 and 38, between gas generating propellants 806and a coolant/filter 807. This inflator is different from the inflatorof FIG. 26 in that the perforated basket 850 is utilized in anelectrically-actuated inflator.

The inflator has a housing which includes a diffuser shell 801 having aplurality of gas diffuser ports 811 and a closure shell 802, which isjoined to the diffuser shell 801 by one of various welding methods. Thehousing has two chambers therein, defined by an approximatelycylindrical separation wall 803 disposed concentrically with a centralopening 813. The separation wall 803 defines an ignition deviceaccommodating chamber 804 and a combustion chamber 805. An ignitiondevice including, for example, a transfer charge 808 and an igniter 812,as described in conjunction with other drawings, is disposed inside theignition device accommodating chamber 804. A perforated basket 850, asshown in FIGS. 37 and 38, and gas generating propellants 806, acoolant/filter 807, a coolant/filter supporting element 809, a ring 810,a plate member 816, and other elements suitable for the actuation of theinflator are installed in the combustion chamber 805. Also, it ispossible to provide, for example, a space 814 outside the coolant/filter807.

The perforated basket 850 is approximately cylindrical in shape and hasa plurality of through-holes 851 in the peripheral wall surface 852 inperipheral and axial directions thereof. The through-holes 851 can beeither formed at a predetermined interval with regularity or randomly.Further, the size of the through-holes 851 can be freely adjusted withinthe range that does not affect the flow of the combustion gas passingtherethrough. The perforated basket 850 is disposed between the gasgenerating propellants 806 and the coolant/filter 807, and covers theentire area where the coolant/filter 807 is exposed. In other words, theperforated basket 850 covers the entire area below a flame resistingplate portion 815 of the coolant/filter supporting element 809. Further,the perforated basket 850 can be designed to have the same or slightlyshorter axial length than that of the coolant/filter 807 such that theperforated basket 850 extends to the outside of the flame resistingplate portion 815 of the coolant/filter supporting element 809, therebyoverlapping with the flame resisting plate portion 815.

The perforated basket 850 can also be utilized in amechanically-actuated inflator as illustrated in FIG. 26.

A Fourteenth Preferred Embodiment

The airbag inflator of the present embodiment, as illustrated in FIG.39, is similar to the airbag inflator as illustrated in FIG. 29. Theinflator of the present embodiment has a perforated basket 850′, asillustrated in FIGS. 40 and 41, between gas generating propellants 806′and a coolant/filter 807′. This inflator is different from the inflatorof FIG. 29 in that the perforated basket 850′ is utilized in anelectrically-actuated inflator.

Similar to the airbag inflator shown in FIG. 36, the inflator of thepresent embodiment has a housing which includes a diffuser shell 801′,having a plurality of gas diffuser ports 811′, and a closure shell 802′joined to the diffuser shell 801′. The closure shell 802′ has a centralopening 813′. The housing has a separation wall 803′ which defines thehousing into two chambers, namely, an ignition device accommodatingchamber 804′ and a combustion chamber 805′. An ignition device,including a transfer charge 808′ and an igniter 812′, as described inconjunction with other drawings, is disposed inside the ignition deviceaccommodating chamber 804′. In addition to the perforated basket 850′,as shown in FIGS. 40 and 41, gas generating propellants 806′, acoolant/filter 807′, a ring 810′, a ring shaped plate member 809′, andother elements suitable for the actuation of the inflator are installedin the combustion chamber 805′. Also, it is possible to provide, forexample, a space 814′ outside the coolant/filter 807′.

In the present embodiment, the perforated basket 850′, disposed betweenthe gas generating propellants 806′ and the coolant/filter 807′, has ashape different from the perforated basket 850 shown in FIG. 36. Asillustrated in FIGS. 40 and 41, the perforated basket 850′ includes aperipheral wall 852′ having a plurality of through-holes 851′, and anapproximately flat circular cap portion 853′ formed at the upper openingof the peripheral wall 852′. The cap portion 853′ may be formed suchthat it engages with an inner surface of an upper circular portion 816′of the housing. Since this particular embodiment has a cylindricalseparation wall 803′, attached to the diffuser shell 801′, for definingthe ignition device accommodating chamber 804′, the cap portion 853′ ofthe perforated basket 850′ has an opening 854′, at the center portionthereof, for inserting the separation wall 803′.

In the perforated basket 850′ of the present embodiment, thethrough-holes 851′ are formed at portions of the peripheral wall 852′other than portions where it radially opposes the through-holes 817′ inthe separation wall 852′. In other words, the basket 850′ can protectthe coolant/filter 807′ from flames spouting from the through-holes 817′due to the combustion of the transfer charge 808′. Further, to deflectthe flames such that the flames sufficiently reach the gas generatingpropellants 806′, the through-holes 851′ in the peripheral wall 852′ ofthe perforated basket 850′ are formed at portions other than where itwould be exposed to the flames from the through-holes 817′ of theseparation wall 803′. Preferably, the through-holes 851′ are formed, atregular intervals, at portions of the periphery wall 852′ below theflame spouting portions of the separation wall 803′. As a result, theupper portion of the perforated basket 850′, more specifically, theportion above the through-holes 851′, has a coolant/filter protectingfunction which protects the coolant/filter 807′ from the flames of thetransfer charge 808′ spouting toward the coolant/filter 807′, and also acombustion enhancing function which deflects the flames such that theflames sufficiently reach the gas generating propellants 806′. As in thecase of the perforated basket as illustrated in FIGS. 37-38, the size ofthe through-holes 851′ can be adjusted in the similar manner.

The perforated basket 850′ can also be used in mechanically-actuatedinflators as shown in FIG. 29.

A Fifteenth Preferred Embodiment

Similar to the airbag inflator as shown in FIG. 33, the airbag inflator,as illustrated in FIG. 42, is characterized in that the coolant/filter750′ consisting of two or more layers, is installed in a housing. Thisinflator is different from the inflator of FIG. 33 in that acoolant/filter 750′ having two or more layers is utilized in anelectrically-actuated inflator.

The inflator of the present embodiment has a housing which includes adiffuser shell 701′, having a plurality of gas diffuser ports 711′, anda closure shell 702′ joined to the diffuser shell 801′. The housing alsohas a separation wall 703′ which defines the housing into two chambers,namely, an ignition device accommodating chamber 704′ and a combustionchamber 705′. An ignition device, including a transfer charge 708′ andan igniter 715′, as described in conjunction with other drawings, isdisposed inside the ignition device accommodating chamber 704′. Inaddition to a coolant/filter 750′ having two or more layers, asillustrated in FIG. 43, gas generating propellants 706′, acoolant/filter supporting element 709′, a ring 710′, a plate member712′, and other elements suitable for the actuation of the inflator areinstalled in the combustion chamber 705′. Also, it is possible toprovide, for example, a space 714′ outside the coolant/filter 750′.

The coolant/filter 750′, consisting of two or more layers, can beconstructed by forming an inner layer 751′ and an outer layer 752′ withdifferent densities or different materials, and superimposing these in aradial direction. When constructing a coolant/filter 750′ with layershaving different densities, the inner layer 751′ can be formed with acoarse metal mesh and the outer layer 752′ can be formed with a finemetal mesh. For the coarse metal mesh used in the metal mesh 751′, anannular metal mesh layer as illustrated in FIGS. 2-6, which is formed bycompressing in a mold, can be used.

The coolant/filter 750′ can also be used in mechanically-actuatedinflators as shown in FIG. 33.

The Non-Azide Gas Generating Material

The conventional azide gas generating material has the decompositioninitiation temperature of 350° C. and the combustion temperature of1500° K and, with an ordinary igniter alone, will therefore result in anunstable ignition. Even if ignited, the gas generating material is notburned in a satisfactory condition to exhibit its full performance.Hence, a transfer charge (B/KNO₃), which is ignited by the igniter togenerate an enough energy to ignite and burn the gas generating materialsatisfactorily, is used.

It has been discovered that the use, as the airbag inflator's gasgenerating material, of a non-azide material, which has thedecomposition initiation temperature of 330° C. or lower, the combustiontemperature of 2000° K or higher and excellent ignition and combustioncharacteristics, can obviate the transfer charge that has been requiredin the conventional airbag inflator. The decomposition initiationtemperature is preferably 310° C. or lower.

The non-azide gas generating material used in this airbag inflator canbe chosen from a variety of conventionally proposed materials, whichinclude: a compound having as major components including an organicnitrogen compound-such as tetrazole, triazole and their metal salts-andan oxygen containing oxidizing agent such as alkali metal nitrate; and acompound which uses triaminoguanidine nitrate, carbohydrazide andnitroguanidine as a fuel and nitrogen source and also nitrate, chlorateand perchlorate of alkali metal or alkaline earth metal as an oxidizingagent. The gas generating material in this invention is not limited tothese but can be selected from other materials as required according tosuch requirements as combustion speed, non-toxicity and combustiontemperature. The gas generating material may be formed into appropriateshapes, such as pellets, wafers, hollow cylinders, porous bodies anddisks.

When the gas generating material is ignited by the igniter, the greaterthe surface area of the gas generating material, the easier it ignites.It is, therefore, desired that the gas generating material be formedinto such shapes as hollow cylinders and porous bodies.

The inner volume of the housing of the airbag inflator is preferably inthe range of 65 to 115 cc, but may be 60 to 130 cc. The amount of chargeof the solid gas generating material is preferably in the range of 30 to40 g for a driver's side airbag, but may be 20 to 50 g.

When an automotive airbag inflator uses a non-azide gas generatingmaterial with the linear burning velocity of 5 to 30 mm/sec under thepressure of 70 kg/cm², it is required that all the gas generatingmaterial be burned completely in 40 to 60 msec for the driver's seatairbag, in 50 to 80 msec for the front passenger seat airbag, and in 5to 15 msec for the side collision airbag. An internal pressure of theinflator may be controlled as a function of the total area of the gasdischarge ports in the diffuser shell. In such a case, to regulate thecombustion of the gas generating material, an appropriate setting ismade of the ratio A/At, where A is the total surface area of the gasgenerating material and At is the total area of the gas discharge portsin the diffuser shell. This ratio A/At is set as follows:

For the driver's seat airbag, A/At=100-300, for 20 to 50 g of gasgenerating material;

For the front passenger seat airbag, A/At=80-240, for 40 to 120 g of gasgenerating material; and

For the side collision airbag, A/At=250-3600, for 10 to 25 g of gasgenerating material.

When the ratio A/At exceeds the maximum value of each airbag, thepressure in the airbag inflator rises excessively, resulting in thecombustion speed of the gas generating material becoming too large. Whenthe ratio is less than the minimum value, the pressure in the airbaginflator does not rise enough, resulting in the combustion speedbecoming too small. In either case, the combustion time falls outside ofthe desired range and the airbag inflator with such combustion times isnot usable.

To achieve complete combustion within a desired combustion time, it isdesired that each piece of the gas generating material have the smallestthickness of 0.01 to 2.5 mm and more preferably 0.01 to 1.0 mm.

Experiments were conducted using four kinds of gas generating material,which were ignited by the igniter using no transfer charge. The resultof experiments is shown in Table 1. The igniter uses Zpp (a mixture ofzirconium/potassium perchiorate) and has an output of 1250 psi. Thecomposition ratio is a weight %. NQ is a high specific gravitynitroguanidine.

TABLE 1 Composition of gas generating material Composition ratioEmbodiment 1 NQ/Sr(NO₃)₂ 55/45 Embodiment 2 NQ/S(NO₃)₂/acid clay35.4/49.6/5/10 /CMC-Na Comparison 1 NaN₃/CuO 61/39 Comparison 2 NQ/CuO26/74

TABLE 2 Decomposition initiation Combustion temperature temperatureIgnition Embodiment 1 200° C. 2362° C. Yes Embodiment 2 210° C. 2270° C.Yes Comparison 350° C. 1148° C. No case 1 Comparison 200° C. 1253° C. Nocase 2

In the embodiment 1 and embodiment 2, the gas generating material wasignited by the igniter without using a transfer charge.

In the comparison case 1, the gas generating material failed to ignitewithout a transfer charge because the decomposition initiationtemperature is high and the combustion temperature is too low.

In the comparison case 2, the gas generating material failed to ignitewithout a transfer charge because the combustion temperature is lowalthough the decomposition initiation temperature is low.

There is a desire to limit the amount of combustion particulatesdischarged with the gas from the discharge (diffuser) ports of theinflator housings because such particulates tend to burn an airbagattached to the inflator. An optimum range of particulates is not toexceed 2 g. It should be noted that the combustion temperature of thegas, per se, is not a critical factor for preventing airbag damage.

The coolant/filters of the present invention must work such that thecombustion particulates contained in an ordinary amount of the gasgenerated by the combustion of the gas generating material when theairbag inflator has worked becomes smaller than 2 g, desirably smallerthan 1 g, and particularly desirably smaller than 0.7 g. Here, theordinary amount of the gas generated will be from 0.5 to 1.5 mols in thecase of the airbag inflator for an airbag for the driver's seat of anautomobile and from 1.5 to 5 mols in the case of the airbag inflator foran airbag for the passenger side seat though it may vary depending uponthe uses, as a matter of course. In the airbag inflator for an airbag ofthe present invention, the amount of the combustion particulatescontained in the generated gas must be limited to the above-mentionedpredetermined value irrespective of the amount of the gas generated. Inthis regard, however, the required number of mols of gas is reducedbecause of the higher combustion temperatures and attendant higherexpanded volume of gas generated by the non-azide gas generatingmaterial. Therefore, less propellant is required and smaller inflatorsare made possible.

The bulk density of such coolant/filters is from 3.0 to 5.0 g/cm³ andpreferably 3.5 to 4.5 g/cm³.

The material of the metal meshes is a stainless steel. As the stainlesssteel, SUS304, SUS310S, SUS316 (specified under JIS), etc., for example,can be used. The SUS304 (18Cr—8Ni—0.06C) is an austenite-type stainlesssteel which exhibits excellent corrosion resistance.

A reinforcing ring having a number of through-holes formed in the entireperipheral wall thereof may be fitted to both or either one of the outerside and the inner side of the coolant/filter, but need not necessarilybe used.

The inflators of the present invention use gas generating material of anon-azide type organic nitrogen compound. The non-azide type gasgenerating material comprises at least an organic nitrogen compound, anoxidizing agent and a slag-forming agent. The gas generating materialmay be blended with a binder when it is to be molded in a desired shape.

As the organic nitrogen compound, any compound selected from the groupconsisting of triazole derivative, tetrazole derivative, guanidinederivative, azodicarbonamide derivative, and hydrazine derivative, or amixture thereof can be used.

Concrete examples include 5-oxo-1,2,4-triazole, tetrazole,5-aminotetrazole, 5,5′-bi-1H-tetrazole, guanidine, nitroguanidine,cyanoguanidine, triaminoguanidine nitrate, guanidine nitrate, guanidinecarbonate, biuret, azodicarbonamide, carbohydrazide, carbohydrazidenitrate complex, dihydrazide oxalate, hydrazine nitrate complex, and thelike. Among them, nitroguanidine and cyanoguanidine are preferred, andnitroguanidine is most preferred for having the least number of carbonatoms in the molecules. The nitroguanidine includes needle-likecrystalline nitroguanidine having a low specific weight and a massivecrystalline nitroguanidine having a high specific weight, and both ofthem can be used. However, the nitroguanidine having a high specificweight is preferred from the standpoint of safety at the time ofproduction in the presence of a small amount of water and easy handling.

The compound is used at a concentration of usually from 25 to 60% byweight and, preferably, from 30 to 40% by weight though it may varydepending upon the numbers of carbon atoms, hydrogen atoms and otherelements to be oxidized in the molecular formula. The concentration of atrace amount of CO increases in the generated gas when the amount of thecompound is larger than a theoretical complete oxidation requirement andthe concentration of a trace amount of NOx increases in the generatedgas when the amount of the compound is equal to, or smaller than, thetheoretical complete oxidation requirement, though the absolute valuemay change depending upon the kind of the oxidizing agent that is used.The most desired range is the one in which an optimum balance ismaintained between the two.

A variety of oxidizing agents can be used such as the one selected fromat least nitrates containing cations of an alkali metal or an alkalineearth metal. The amount of its use is from 40 to 65% by weight and,particularly, from 45 to 60% by weight from the standpoint of theconcentrations of the above-mentioned CO and NOx, though the absolutevalue may differ depending upon the kind and amount of the gasgenerating compound.

Oxidizing agents such as nitrite and perchlorate that are much used inthe field of airbag inflators can also be used. It is, however, desiredto use a nitrate from such a standpoint that the number of oxygen atomsdecreases in the nitrite molecules compared with that of the nitrate andthat fine powdery mist that tends to be emitted out of the bag is formedin a decreased amount.

The slag-forming agent works to transform the oxides of alkali metals oralkaline earth metals formed by the decomposition of the oxidizing agentcomponent in the gas generating material composition into a solid from aliquid to permit the coolant/filter to better confine them in thecombustion chamber, so that they will not be emitted in the form of amist from the inflator. The coolant/filter intercepts the mix ofslag-forming agent and powdery residue to cool it and cause it to buildinto particle sizes which cannot then pass through the coolant/filter.It is this interaction which eliminates the need for a conventionalfilter structure. An optimum slag-forming agent can be selecteddepending upon the metal components. Examples of the slag-forming agentinclude natural clays containing aluminosilicate as a main component,such as bentonite and kaolin, artificial clays such as synthetic mica,synthetic kaolinite and synthetic smectite, and talc which is a hydratedmagnesium silicate mineral. Any one of them can be used as theslag-forming agent. A preferred example of the slag-forming agent is anacid clay.

A mixture of oxides of three components of a calcium oxide, generatedfrom a calcium nitrate, an aluminum oxide, which is a chief component ofa clay, and a silicon oxide, exhibits a viscosity of from about 3.1poises to about 1000 poises over a temperature range of from 1350° C. to1550° C., and a melting point of from 1350° C. to 1450° C. dependingupon the composition ratios. By utilizing these properties, theslag-forming performance is exhibited depending upon the mixingcomposition ratio of the gas generating material composition.

The slag-forming agent is used in an amount of from 1 to 20% by weightand, preferably, from 3 to 7% by weight. When used in too large amounts,the linear burning velocity decreases and the gas generating efficiencydecreases. When used in too small amounts, the slag-forming performanceis not exhibited to a sufficient degree.

The binder is necessary for obtaining a desired molded article of a gasgenerating material composition. Any binder can be used provided itexhibits viscosity in the presence of water and solvent withoutadversely affecting the combustion behavior of the composition. Examplesof the binder may include polysaccharide derivatives such as metal saltsof carboxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate,cellulose propionate, cellulose acetate butyrate, nitrocellulose, starchand the like. Among them, however, a water-soluble binder is preferredfrom the standpoint of safety in the production and easy handling. Therecan be preferably exemplified a metal salt of carboxymethyl celluloseand, particularly, sodium salt.

The binder is used in an amount of from 3 to 12% by weight and, morepreferably, from 4 to 12% by weight. When the binder is used on the sideof large amounts, the molded article exhibits an increased breakdownstrength. The numbers of carbon atoms and hydrogen atoms in thecomposition increase with an increase in the amount of the binder,resulting in an increase in the concentration of a trace amount of COgas which is a product of incomplete combustion of carbon anddeteriorates the quality of the generated gas. When the binder is usedin an amount in excess of 12% by weight, in particular, the oxidizingagent must be used at a relatively increased ratio, whereby the ratio ofthe gas generating compound relatively decreases, making it difficult toestablish a practicable inflator system.

Furthermore, the subsidiary effect of a sodium salt of carboxymethylcellulose is that when a molded article is produced by using water, thesodium nitrate formed by the metal exchange reaction with the nitratewhich exists in a minute form of a size of molecules causes thedecomposition temperature of the nitrate which is the oxidizing agentand, particularly, of the strontium nitrate having a high decompositiontemperature to be shifted toward the low temperature side, contributingto enhancing the combustibility.

Therefore, a preferred gas generating material composition used forputting the present invention into practice comprises:

(a) about 25 to 60% by weight and, preferably, 30 to 40% by weight of anitroguanidine;

(b) about 40 to 65% by weight and, preferably, 45 to 65% by weight of anoxidizing agent;

(c) about 1 to 20% by weight and, preferably, 3 to 7% by weight of aslag-forming agent; and

(d) about 3 to 12% by weight and, preferably, 4 to 12% by weight of abinder, and particularly preferably comprises:

(a) about 30 to 40% by weight of a nitroguanidine;

(b) about 40 to 65% by weight of a strontium nitrate;

(c) about 3 to 7% by weight of acid clay; and

(d) about 4 to 12% by weight of a sodium salt of carboxymethylcellulose.

According to the present invention, therefore, there is provided amolded article of a gas generating material for an airbag comprising:

(a) about 25 to 60% by weight of a nitroguanidine;

(b) about 40 to 65% by weight of an oxidizing agent;

(c) about 1 to 20% by weight of a slag-forming agent; and

(d) about 3 to 12% by weight of a binder.

As an organic nitrogen compound, dicyandiamide can also be preferablyused.

The gas generating material composition contains the organic nitrogencompound in such an amount that the oxygen balance is most desirablybrought near to zero by a proper combination of an oxidizing agent orother additives, though the amount of the organic nitrogen compound mayvary depending upon the numbers of atoms and molecular weight of thenitrogen compound and upon the oxidizing agent and the additives. Amolded article of an optimum composition can be obtained by adjustingthe oxygen balance toward the positive side or the negative sidedepending upon the concentration of trace amounts of CO and NOx that aregenerated. When the dicyandiamide is used, for example, its amount willpreferably be from 8 to 20% by weight.

The oxidizing agent, containing oxygen, used in the present inventionwill be the one that has been widely known in the field of gasgenerating materials for airbags. It is, however, desired to use anoxidizing agent of which the residue basically assumes the liquid orgaseous form and which forms a high-melting substance so will not toexert thermal load upon the coolant/filter.

For example, the potassium nitrate is an oxidizing agent which isgenerally used for the gas generating materials. However, the potassiumnitrate is not desirable from the standpoint of thermal load upon thecoolant/filter, since the principal particulates thereof after thecombustion is potassium oxide or potassium carbonate, the potassiumoxide decomposing into potassium peroxide and metal potassium at about350° C., and the potassium peroxide exhibiting a melting point of 763°C. to assume the liquid or gaseous form in the state where the airbaginflator is operated.

The oxidizing agent preferably used in the present invention may be astrontium nitrate. The particulates after the combustion of thestrontium nitrate is a strontium oxide having a melting point of 2430°C., which remains almost in a solid state even in a state where theairbag inflator has operated.

There is no particular limitation to the amount of the oxidizing agentused in the present invention provided that it is used in an amountsufficient for completely burning the organic nitrogen compound. Theamount can be suitably changed for controlling the linear burningvelocity and the amount of generated heat. When the strontium nitrate isused as the oxidizing agent for the dicyandiamide, it is desired thatits amount is from 11.5 to 55% by weight.

A preferred gas generating material composition of the present inventioncontains 8 to 20% by weight of dicyandiamide, 11.5 to 55% by weight ofstrontium nitrate, 24.5 to 80% by weight of copper oxide, and 0.5 to 8%by weight of a sodium salt of carboxymethyl cellulose. The presentinvention, however, further provides a gas generating materialcomposition containing 8 to 20% by weight of dicyandiamide, 11.5 to 55%by weight of strontium nitrate, 24.5 to 80% by weight of copper oxide,and 0.5 to 8% by weight of a sodium salt of carboxymethyl cellulose.

A non-azide solid gas generating material, comprising nitroguanidine,Sr(NO₃)₂, carboxymethyl cellulose, and acid clay at % by weight ofnitroguanidine:Sr(NO₃)₂:carboxymethyl cellulose:acid clay=35.4:49.6:10:5was ignited in an airbag inflator of the present invention in a tank togenerate a gas. The gas generated from the airbag inflator was containedin the tank which was then washed with acetone to collect combustionparticulates contained in the gas discharged through the gas diffuserports of the inflator into that tank, in order to measure the amount ofthe combustion particulates residing in that gas.

As a result, the amount of the gas discharged through the diffuser portsof the airbag inflator was one mol, and 0.3 g of combustion particulateswere contained therein.

An airbag inflator of the present invention for a passenger side airbagin a similar test produced gas in an amount of 4 mols containing 0.6 gof combustion particulates. Both of these tests show production of lessthan 2 g of particulates and hence, such results preclude particulatedamage to airbags.

Additional Operating Parameters

Inventors have discovered that to stably burn the non-azide gasgenerating material, the maximum pressure inside the airbag inflatormust be at least 100 kg/cm² and that, when the maximum internal pressureexceeds 300 kg/cm², the housing of the airbag inflator is required tohave an excessively large strength, thus making it difficult to reducethe size and weight of the airbag inflator.

Further, the inventors have found that there is no need for pressurecontrol on the maximum internal pressure of the inflator by a dischargeimpeding fracture plate or the like and that if a small housing (with aninner volume less than 120 cc) has the maximum internal pressure in therange of from 100 to 300 kg/cm² and the total area of the openings/gasgeneration in the range of from 0.50 to 2.50 cm²/mol, a desired outputcurve for inflating the airbag can be obtained.

In other words, the present invention provides an airbag inflator, whichaccommodates a gas generating material in the housing and has aplurality of openings to allow the gas generated from combustion of thegas generating material to flow into the airbag. This airbag inflator ischaracterized in that the total area of the openings per unit volume ofthe generated gas is 0.50 to 2.50 cm²/mol and the maximum internalpressure during operation of the airbag inflator is 100 to 300 kg/cm².

In implementing this invention, the openings each preferably have anequivalent circle diameter of 3 to 4.5 mm. The word equivalent circlediameter is used instead of a diameter because the openings may have, inaddition to a true circle, a shape that can be approximated to a circle.This represents a diameter of a true circle that has an area equal tothat of the opening in question. For the equivalent circle diameter ofthe openings less than 2 mm, even if the total area of the openings perunit volume of generated gas is 2.50 cm²/mol or less, the airbag partslocated at the outlet of the openings—an airbag if the openings are gasdiffuser ports of the diffuser of the housing or a coolant/filter if theopenings are a combustion chamber wall inside the housing—will bedamaged. Increasing the number of openings to prevent this damageresults in an increase in the manufacture cost.

In the present invention, selection of the non-azide gas generatingmaterial is made and the diameter and number of the openings isdetermined in such a way that, in a small housing with an internalvolume of 120 cc or less, the maximum internal pressure is controlled inthe range of 100 to 300 kg/cm², preferably 130 to 180 kg/cm², and thetotal area of the openings per unit volume of generated gas in the rangeof 0.50 to 2.50 cm²/mol, preferably 1.00 to 1.50 cm²/mol. Thisarrangement provides an output curve suited for inflating the airbag.The total area of the openings is determined from (one holearea)×(number of holes).

The airbag inflator of this invention needs only to have a construction,in which a plurality of openings for controlling the combustion of thegas generating material accommodated in the housing are formed in thehousing or a separation wall in the housing (simply referred to as anin-housing separation wall) so that a gas produced from the gasgenerating material flows through the openings into the airbag. Theopenings each have an area equivalent to the area of a circle 3 to 4.5mm in inner diameter. It is preferred that a total of 12 to 20 suchopenings be formed in the housing or the in-housing separation wall, orboth, and arranged in the circumferential direction. The maximuminternal pressure during the operation of the airbag inflator isdetermined by the openings formed in either the housing or thein-housing separation wall or by the openings formed in both the housingand the in-housing separation wall. For example, when the openings areformed in both the housing and the in-housing separation wall and theinner pressure of the housing is controlled by the openings in one ofthe housing and the separation wall, it is possible to appropriatelyform the openings of the other one of the housing and the separationwall as long as they do not put a further control on the inner pressure.

The openings, through which the generated gas passes, may be arranged ina row or in a stagger in the circumferential direction of the housingand/or the in-housing separation wall.

The housing can be formed by casting or forging. It can also be formedby welding, which involves pressing a diffuser shell having openings fordischarging gas (gas discharge ports) and a closure shell having acenter hole, and joining them together by welding, such as plasmawelding, friction welding, projection welding, electron beam welding,laser welding, and TIG arc welding. The housing has gas discharge ports.The housing formed by pressing is easy to manufacture and has reducedmanufacturing cost. The diffuser shell and the closure shell may beformed of, for example, a stainless steel plate 1.2 to 2.0 mm thick,with the cuter diameter of the diffuser shell set to 65 to 70 mm and theclosure shell to 65 to 75 mm. A steel plate plated with nickel may beused instead of the stainless steel plate. It is preferred that thehousing be formed with a mounting flange and that a narrow space 1.0 to4.0 mm thick be formed as a gas passage between the housing innercircumferential wall and the coolant. The overall height of the housingis preferably set at 30 to 35 mm.

The separation wall is provided in the housing, as required, fordividing the interior of the housing into two or more chambers. In thisinvention, the separation wall, which is formed with a plurality ofopenings that control the combustion of the gas generating material, isa separation wall through which the gas generated from the gasgenerating material in the combustion chamber passes. Such a separationwall includes a separation wall disposed between the gas generatingmaterial accommodating chamber in the housing and the coolant/filter,and a combustion ring. The combustion ring is installed in the housingand surrounds the combustion chamber and has a number of openings formedin its circumferential wall to control the maximum inner pressure duringthe combustion of the gas generating material.

The separation wall can also be formed by installing a cylindricalmember in the housing and using its circumferential wall as theseparation wall. The cylindrical member may be constructed by rolling astainless steel plate of 1.2 to 2.0 mm thick into a tube and welding it.When the cylindrical member is used as the separation wall, it is alsoformed with openings.

When it is necessary to prevent entry of outside air (moisture), it isdesired that the openings be sealed with a seal tape having a width of 2to 3.5 times the diameter of the openings. The seal tape is designed toprevent ingress of moisture by closing the openings and does not presentany hindrance against the generated gas passing through the openings nordoes it control the internal pressure of the housing. Hence, the sealtape need only have a thickness sufficient to prevent entry of moisture.When an aluminum tape is used as the seal tape, the tape thickness isset to 25 μm or more, for example, to block entry of moisture via thetape surface. In this invention, however, because the maximum internalpressure of the housing is controlled solely by the total area of theopenings in order to ensure quick activation of the airbag inflator,when the aluminum tape thickness is 80 μm or greater, the tape becomesdifficult to break even by the ejecting gas from the combustion of thegas generating material and takes some time to break, thus delaying theactivation of the airbag apparatus. This may result in a failure toachieve an intended performance of the apparatus. Thus, when an aluminumtape is used as a seal tape, the tape thickness is desirably set to 25to 80 μm.

ADVANTAGES AND EFFECTS OF THE INVENTION

In the airbag inflator of the present invention, the housing is formednot by costly forging, but by pressing, which is less expensive andeasier to manufacture. The airbag inflator of this invention istherefore advantageous in terms of cost and manufacturability. That is,by pressing the diffuser shell and the closure shell, the manufacturecost is reduced and the manufacture of these shells made easy.

Because the central cylinder member, which has been formed integral withthe circular portion of the diffuser shell in the conventional airbaginflator, is formed separately, the shape of the diffuser shell can bemade simpler. The separate forming of the central cylinder member andthe diffuser shell allows the volume of the central cylinder member tobe changed as required independently of the diffuser shell. The centralcylinder member can be formed as a single component at low cost by, forexample, the UO pressing method.

Because the coolant/filter of the airbag inflator of this invention has,in addition to the cooling function, a function of defining thecombustion chamber and a function of arresting combustion particulates,it is possible to eliminate the combustion chamber separation wallmember and the filter, both of which have been provided in addition to acoolant in conventional airbag inflators. This reduces the number ofcomponents and also the diameter of the airbag inflator, thus realizinga small, lightweight airbag inflator.

The airbag apparatus having this airbag inflator has a reduced number ofcomponents in the airbag inflator and a reduced diameter of the airbaginflator. Thus, a small, lightweight airbag apparatus can be realized.

More specifically, the coolant/filter structure of the presentinvention, constituted as described above, is capable of effectivelyentrapping even fine combustion particulates. That is, thecoolant/filter exhibits an excellent entrapping function in addition toits cooling function, and makes it possible to omit the filter that waspreviously needed in addition to a coolant.

Furthermore, the coolant/filter structure of the present invention makesit possible to define a pressure chamber such as combustion chamber ofthe airbag inflator. This makes it possible to omit members for definingthe combustion chamber such as combustor cups, combustion rings, etc.that were previously needed in addition to a coolant.

Therefore, the airbag inflator, equipped with the coolant/filter deviceof the present invention, uses a decreased number of parts, has adecreased diameter, and can be smaller in size and decreased in weightfrom conventional inflators.

The coolant/filter device having a predetermined bulk density exhibitsvery increased shape-retaining strength, is not readily deformed by thegas pressure, maintains a proper combustion particulates-entrappingfunction, and can be of decreased thickness from conventional coolantand/or filter devices.

Desirably, furthermore, the coolant/filter of the present invention hasa swell-suppressing means formed on the outer periphery thereof andmaintains a gap or space between the filter of the gas generator and thehousing during operation of the airbag inflator.

By maintaining a space between the coolant/filter and the housing, thecombustion gas flows through the entire area of the coolant/filterstructure. Therefore, the coolant/filter is effectively used, and aneffective cooling and purification of the gas is obtained.

Because the airbag inflator of this invention is constructed asdescribed above, the combustion gas passes through the entire area ofthe coolant/filter structure realizing efficient utilization of thecoolant/filter and effective cooling and cleaning of the combustion gas.

The perforated basket protects the inner surface of the coolant/filterfrom melting without affecting the pressure inside the inflator.Further, the perforated basket prevents direct contact of thecoolant/filter and the gas generating propellants, and also prevents thepropellants from rubbing against the coolant/filter due to vibration.

The flame-preventing portion of the perforated basket or theflame-preventing plate, which is disposed opposing the row ofthrough-holes in the separation wall, covers the inner peripheralsurface of the coolant/filter from flame that gushes toward thecoolant/filter, and further causes the gushing flame to be deflected sothat the flame sufficiently reaches the gas generating material.Further, by forming the flame-preventing portion and the perforatedportion as a unit, a manufacturing process can be reduced and an elementfor connecting the perforated portion to the flame-preventing portioncan be eliminated.

The airbag inflator of this invention obviates the need for a transfercharge that has been used in conventional airbag inflators. Comparedwith a conventional three-chamber airbag inflator, the airbag inflatorof this invention has a reduced diameter, realizing reductions in sizeand weight. Further, the common igniter/combustion chamber airbaginflator of this invention having no separation wall for enhancer, andhaving gas generating propellants surrounding the igniter, within thehousing, has simplified shapes of the diffuser shell and closure shellthat form the housing, which in turn makes the airbag inflator smaller,lighter, and easier to manufacture and less costly.

Sensing a shock due to a collision by the mechanical-type sensorinstalled within the airbag inflator of the present invention obviatesthe electric shock sensor, the electronic control unit, and harnessesconnecting the sensor and the control unit, thereby making the airbagapparatus more compact and lighter in weight as compared to theelectrically activated airbag apparatus.

The airbag inflator of the present invention can either be actuated byelectrically or mechanically sensing a shock due to a collision.

The airbag inflator of this invention uses a non-azide gas generatingmaterial. By controlling the diameter of the openings, through which thegenerated gas flows into the airbag, and also the total area ofopenings/amount of gas generated, it is possible to burn the gasgenerating material stably without using a fracture plate and therebyproduce an output curve optimal for inflating the airbag folded in asmall container. This invention, therefore, is advantageous in reducingthe size and weight of the airbag inflator.

More specifically, the airbag inflator for an airbag of the presentinvention uses a non-azide type gas generating material compositioncontaining an organic nitrogen compound, an oxidizing agent and acidclay as essential components, and further uses a coolant/filter having abulk density of 3.0 to 5.0 g/cm³. Therefore, even when liquid combustionparticulates are generated by the combustion of the gas generatingmaterial, a slag is formed which is then filtered by the coolant/filterdevice in the airbag inflator of the present invention. As a result, aminimum amount of combustion particulates pass through thecoolant/filter device, and do not cause damage to the airbag.

In the airbag apparatus using the airbag inflator of the presentinvention, the airbag is not damaged by combustion particulates. Thus,the airbag apparatus is suited for mounting on automobiles, aircraft,etc. to protect human body.

The airbag inflator of this invention has short pass prevention means ofthe above construction to prevent a short pass of the combustion gas toensure that all the combustion gas passes through the coolant/filterdevice, thus effectively cooling and cleaning the combustion gas andassuring normal unfolding of the airbag.

Because of the various constructions described above, the airbaginflator of this invention can burn the gas generating materialcompletely and predictably within a desired length of time.

In the airbag inflator of this invention, the construction of the flangeportions in the foregoing embodiments prevents excessive deformation ofthe housing at the time of activation of the airbag inflator, ensuringnormal combustion of the gas generating means and normal flow of thecombustion gas, which in turn permits reduction of the thickness of thehousing, thereby permitting reductions in size and weight of the airbaginflator.

The flange portion provided on the diffuser shell eliminates the dangerof the passenger on the airbag side being injured should the weldedportion be broken.

Forming the diffuser shell and the closure shell by pressing realizes areduction in the manufacture cost and also facilitates the manufactureof the diffuser shell and closure shell.

One or both of the circular portions of the diffuser shell and theclosure shell are provided with reinforcement ribs or a reinforcementstepped portion, or both, to prevent deformation of the housing,particularly its circular portions, when the airbag inflator isactivated. This in turn prevents a short pass of combustion gas betweenthe inner surfaces of the circular portions and the end faces of thecoolant/filter device, thus assuring normal unfolding of the airbag whenactivated.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. An inflator for an airbag, comprising: a housinghaving gas-discharge ports; an ignition device provided within saidhousing; a gas-generating material provided around said ignition device,said gas generating material being ignited by said ignition device toproduce a combustion gas; and a coolant/filter device provided aroundsaid gas-generating material and adapted to at least one of cool andfilter the combustion gas, said coolant-filter device being made ofmetal meshes and having a bulk density of 3.0-5.0 g/cm³.
 2. The inflatorof claim 1, wherein said gas generating material is a solid non-azidegas generating material.
 3. The inflator of claim 1, wherein saidcoolant/filter device has a substantially annular configuration and madeof stainless steel metal meshes compressed in both radial and axialdirections to provide the bulk density before providing thecoolant/filter within said housing.
 4. The inflator of claim 1, whereinsaid coolant/filter device is formed of flat-plaited metal mesheslaminated in a radial direction.
 5. The inflator of claim 1 wherein themetal meshes have a wire diameter of 0.3-0.6 mm.
 6. The inflator ofclaim 1, further comprising: an inner cylinder disposed in said housing,said inner cylinder defining an ignition device accommodating chamberfor installing said ignition device therein, and a combustion chamberfor storing said gas-generating material and said coolant/filter device.7. The inflator of claim 1, wherein said coolant/filter device isobtained by forming stainless steel meshes into a cylinder, repetitivelyfolding one end portion of the cylinder outwardly to form an annularmulti-layer body, and compressing the multi-layer body in both axial andradial directions in a die.
 8. The inflator of claim 1, wherein saidcoolant/filter device is obtained by forming stainless steel meshes intoa cylinder, pressing the cylinder in a radial direction to form a platemember, rolling the plate member into a multi-layer cylinder body, andcompressing the multi-layer cylinder body in both axial and radialdirections in a die.
 9. The inflator of claim 1, wherein saidcoolant/filter device includes metal meshes of a wire diameter of 0.3 to0.6 mm, and has at an inside thereof a layer of a thickness of 1.5 to2.0 mm made of metal meshes of a wire diameter of 0.5 to 0.6 mm.
 10. Theinflator of claim 1, wherein said coolant/filter device is obtained bylaminating flat-plaited metal meshes of a wire diameter of 0.3 to 0.6 mmin a radial direction and compressing them in radial and axialdirections.
 11. The inflator of claim 1, wherein an outer periphery ofsaid coolant/filter device includes a swell suppressing layer forpreventing said coolant/filter device from swelling when the combustiongas passes therethrough.
 12. The inflator of claim 11, wherein saidswell suppressing layer is a metal mesh layer formed on an outerperipheral surface of said coolant/filter device and has a pressure lossbeing smaller than the coolant/filter device.
 13. The inflator of claim11, wherein said swell suppressing layer includes a perforated cylinderfitted over an outer peripheral surface of said coolant/filter device.14. The inflator of claim 1, further comprising: a space defined in anouter side of said coolant/filter device within said housing, said spacebeing a continuous space adjacent to the gas discharge ports andarranged such that the combustion gas passes an entire portion of saidcoolant/filter device.
 15. The inflator according to claim 14, wherein aradial cross-section of said annular space St is equal to or greaterthan a total open area of the gas discharge ports At.
 16. The inflatorof claim 15, wherein a ratio of the area St to the sum of area At,St/At, is between 1 and
 10. 17. The inflator of claim 16, wherein aratio of the area St to the sum of area At, St/At, is between 2 and 5.18. The inflator of claim 1, wherein said gas generating material is anon-azide gas generating material including an organic nitrogencompound.
 19. A coolant/filter device used in an air bag inflator forproducing a combustion gas to inflate an air bag, said coolant/filterdevice confining a gas generating material in an inflator housing andadapted to cool and filter the combustion gas, comprising: metal meshesradially laminated in an annular configuration and compressed in bothradial and axial directions to provide a predetermined bulk density atleast prior to being placed in the inflator housing.
 20. Thecoolant/filter device of claim 19, wherein the desired bulk density ofsaid coolant/filter device is 3.0-5.0 g/cm³.
 21. The coolant/filterdevice of claim 19, wherein said coolant/filter device is formed offlat-plaited metal meshes including metal wires laminated in an radialdirection.
 22. The coolant/filter device of claim 19, wherein said metalmeshes have a diameter of 0.3-0.6 mm.
 23. A method of forming an annularcoolant/filter device for an air bag inflator for at least one ofcooling a combustion gas produced by a combustion of a gas generatingmaterial provided within an inflator housing and filtering combustionparticulates contained in the combustion gas, comprising: providing asheet of metal meshes; forming said sheet into a cylinder; repetitivelyfolding one end of said cylinder outwardly toward an opposite endthereof to form an annular multi-layer body; and compressing saidmulti-layer body in a forming die in both radial and axial directions toprovide a predetermined bulk density.
 24. The method of claim 23,wherein the predetermined bulk density imparted to said coolant/filterdevice is from 3.0 to 5.0 g/cm³.
 25. The method of claim 23, whereinsaid metal meshes are formed of stainless steel wires having a diameterof 0.3 to 0.6 mm.
 26. The method of claim 23, further comprising:providing an external swell suppressing layer on an outer periphery ofsaid coolant/filter device in order to prevent said coolant/filterdevice from swelling when the combustion gas passes therethrough. 27.The method of claim 26, wherein said external swell suppressing layer isa perforated cylinder which fits around said annular coolant/filterdevice.
 28. A method of forming an annular coolant/filter device for anair bag inflator for at least one of cooling a combustion gas producedby a combustion of a gas generating material provided within an inflatorhousing and filtering combustion particulates in the combustion gas,comprising: rolling a plate member made of metal meshes into a firstmulti-layer cylindrical body; and compressing said first multi-layercylindrical body in a forming die in radial and axial directions toimpart desired bulk density.
 29. The method of claim 28, furthercomprising: forming at least a first metal mesh cylinder formed of metalwire having diameters of 0.3 to 0.6 mm; forming at least a second metalmesh cylinder formed of metal wire having diameters of 0.5 to 0.6 mm;and fitting at least the second metal mesh cylinder to an inside of thefirst metal mesh cylinder to define an inner layer of the annularcoolant/filter device.
 30. The method of claim 28, further comprising:repetitively folding one end of the first multi-layer cylindrical bodyand toward the other end thereof to form a second multi-layercylindrical body.
 31. The method of claim 28, wherein the desired bulkdensity imparted to said coolant/filter device is from 3.0 to 5.0 g/cm³.32. The method of claim 28, wherein said metal meshes are formed ofstainless steel wires having a diameter of 0.3 to 0.6 mm.
 33. The methodof claim 28, further comprising: providing an external swell suppressinglayer on an outer periphery of said coolant/filter device to preventsaid coolant/filter device from swelling when the combustion gas passestherethrough.
 34. The method of claim 33, wherein said external swellsuppressing layer is a perforated cylinder fitted around said annularcoolant/filter device.
 35. The method of claim 28, further comprising:forming the metal meshes into a cylinder prior to the compressing step;and pressing said cylinder in a radial direction to form said platemember.